Inventory has duality. On the one hand, it ensures normal production activities, on the other hand, it is the burden of production, which in itself constitutes a pair of contradictions. Therefore, logistics experts at home and abroad have always focused on inventory. Inventory control is obviously the core of inventory management. This paper introduces a new inventory control method to solve the inventory problem in supply chain. With the development of economy, China logistics has entered a new development period-supply chain era. During this period, China logistics faces two major problems: first, the new logistics system has not been fully established, and logistics integration still needs a process; Second, the traditional logistics still has great shortcomings, and transportation and storage have not been optimally controlled. Therefore, on the one hand, we should try our best to update our ideas and meet the arrival of a new round of logistics revolution. More importantly, we must solve the problems existing in traditional logistics, so as to make China logistics develop healthily and orderly. In traditional logistics, inventory accounts for a large proportion, and it is also a function with the most problems in logistics. Out-of-date inventory will not only occupy too much capital, but also lead to low capital turnover rate. What's more, it will make products become a pile of waste products due to expiration or elimination, which is particularly prominent in the current "buyer's market". So far, most enterprises at home and abroad still adopt traditional inventory control methods for how to control inventory. However, after years of practice, it has been proved that the inventory control method originally proposed relative to "mass production" can no longer adapt to the current "flexible production mode". The author believes that production (or sales) determines inventory-how much inventory is needed to meet production demand, and production mode (or sales mode) determines inventory control mode-what kind of production mode must have what kind of inventory control mode to adapt to it. 1 Traditional inventory control methods and theories are insufficient. For a long time, people have been committed to establishing various models to better control the inventory, hoping to solve the inventory problem through these models. During this period, quantitative ordering method and regular ordering method are highly regarded as two classic inventory control methods. However, practice has proved that these two inventory control methods are simple and feasible in theory, but they have exposed many disadvantages in practice, especially with the rapid development of today's economy, which has gradually changed from the past "seller's market" to the present "buyer's market". It is increasingly found that only establishing several sets of models can not achieve the ideal inventory control state. This is mainly because: ① the original inventory control method has poor real-time performance. Whether it is quantitative ordering method, regular ordering method or various existing inventory control methods, the determination of ordering point is limited to the consumption of inventory in the warehouse, which has nothing to do with production, or although the production of the enterprise is investigated, due to the inherent defects of its model, the ordering point of this period can only be determined according to the production demand of the previous period or earlier, but the real-time ordering cannot be realized, and the ordering time cannot be determined according to the production demand of this period, which cannot be said to be the most primitive inventory control method. It is decided that enterprises adopting these methods are subject to the model everywhere when managing inventory, and cannot give full play to people's subjective initiative, thus becoming "slaves" of the model, leading to passivity and failure everywhere in the ever-changing "buyer's market" at present. ② The concept of inventory management is backward. The traditional inventory management is usually the enterprise's own inventory: each enterprise manages its own inventory, which easily leads to the "bullwhip effect" between upstream and downstream enterprises, and it is difficult to achieve optimal inventory control. This is more prominent after the formal formation of the supply chain. At present, in order to solve this problem effectively, most enterprises have accepted the idea of VMI. 2 New inventory control methods in the supply chain environment A complete supply chain should be composed of the following main members: suppliers, manufacturers, distributors and consumers. And when the logistics develops to a certain stage, the physical delivery between these four parties should be operated by professional logistics companies. Therefore, for the convenience of discussion, all the following are replaced by logistics companies and enterprises. 2. 1 theoretical basis of new inventory control method The traditional inventory management theory holds that the inventory should be entirely borne by the enterprise itself, while the current popular supplier management inventory means that the supplier should manage the inventory for the "users". The author thinks that although VMI is more advanced in theory and can solve many difficulties of traditional inventory management, its role in practical operation needs further verification. Usually, the inventory of an enterprise should be composed of two parts: safety inventory and batch inventory. The former directly determines the service level of the enterprise, or effectively ensures the smooth production and sales of the enterprise. According to the characteristics of these two types of inventory, it can be considered that it will be more realistic and effective if enterprises provide their own safety inventory and logistics companies provide bulk inventory for enterprises. 2.2 A new inventory control method This inventory control method mainly consists of an inventory early warning time system. It means that when an enterprise finds that this batch of "bulk inventory" needs to be replenished, it sends an "early warning instruction" to the logistics company, asking the logistics company to immediately send the next batch of bulk inventory for replenishment. In this process, when the enterprise issues the delivery instruction becomes the key, which we call the inventory early warning time point. Obviously, the inventory early warning time point can not be obtained too early, but it can not be too late. If it is too early, then when the logistics company delivers the goods, the enterprise will bring its own warehouse to accommodate these goods, which violates the original intention of the enterprise to require the minimum inventory; If it is too late, the logistics company will not have enough time to prepare and deliver the goods, which will inevitably lead to the goods not arriving in time, thus causing the enterprise to suffer certain losses. It can be seen that the most critical part of the inventory early warning time system is the inventory early warning time point, and whether its determination is reasonable or not directly affects whether the system can play its best role. Therefore, we must investigate the whole "process" to determine a reasonable early warning time. After analysis, the specific algorithm of early warning time TW is as follows: ① Assuming that the bulk inventory provided by logistics companies to enterprises is QK, this value should be a constant value in the long-term cooperation between logistics companies and enterprises. It should be emphasized that in this method, the enterprise provides its own safety inventory, while the bulk inventory is provided to the enterprise by the logistics company. Therefore, the determination of inventory warning time can only be based on batch inventory, but not on the sum of batch inventory and safety inventory. (2) Assume that the speed of "parts" required for enterprise production is R, referred to as production speed (for sales enterprises, it is sales speed). (3) Assuming that the early warning lead time is t, the early warning lead time refers to the length of time from the enterprise issuing an early warning to the complete use of the batch inventory. The formula T=-t shows that when a logistics company delivers a batch of goods to an enterprise, the enterprise should send a delivery instruction to the logistics company for the next batch of goods at the moment when the goods are put into use. Among the three assumptions for determining the early warning time, the batch inventory QK and the productivity R are stable, or the enterprise can grasp them, because when the enterprise adopts assembly line production, the productivity R becomes a fixed value. But the third hypothesis, that is, the early warning lead time, is unknown to enterprises. The size of early warning lead time directly affects the determination of early warning time. Therefore, we must study the early warning lead time to ensure that it will not have a greater negative impact. After analysis, the determination of early warning lead time depends on the following factors:

① Output R. This is an important tool for enterprises to determine the early warning lead time, which can be determined.

② Stocking efficiency of logistics companies. The higher the stocking efficiency of logistics companies, the shorter the lead time of early warning, and the longer the period for enterprises to issue "early warning instructions".

(3) distance. The farther the distance between logistics companies and enterprises is, the longer the early warning lead time should be.

(4) Transportation speed. What kind of transportation will directly affect the early warning time. The faster the means of transportation, the shorter the early warning lead time, which requires closer cooperation between logistics companies and enterprises.

From the above analysis, it can be seen that enterprises cannot fully grasp the latter three factors, but as long as enterprises and logistics companies cooperate for a period of time, the two sides can form a certain tacit understanding, and they will well grasp the changing law of early warning lead time. Moreover, even if the early warning lead time is really mishandled, I believe the error will not be too great. At this time, the enterprise can completely solve it through its own safety inventory. 2.3 The problems that should be paid attention to in the implementation of the new inventory control method can be seen from the above analysis that this control method is very real-time and very strict in time. Logistics companies and enterprises must cooperate closely to ensure the timely delivery of goods. At the same time, the statistics of some data depend on computers. Therefore, in order to use this inventory control method, enterprises must first do their own information construction, especially their own MIS. Secondly, the information transmission between enterprises and logistics companies should be "electronic" and transmitted in the form of "electronic flow", which can not only improve the speed of information circulation, but also reduce the transaction costs of both parties. At present, both logistics companies and enterprises should adopt EDI, and information can be transmitted through VAN (Value Added Network), which can not only improve the response speed of both parties, but also be safe and reliable. In the near future, when Internet e-commerce is mature, information transmission between enterprises and logistics companies should adopt Internet e-commerce, which can greatly reduce transaction costs.

Inventory early warning time system can effectively ensure that logistics companies can supply goods to enterprises at any time and in time, and it has strong practical operation. At present, Dongyue Automobile Manufacturing Co., Ltd. (Yantai Branch of Shanghai General Motors Manufacturing Co., Ltd.) and Haitong Logistics Co., Ltd. have adopted this system for supply. From the cooperation of more than half a year, there is no mistake, and the inventory cost of Dongyue Company is greatly reduced. It can be said that the inventory control method based on the inventory early warning time system will surely become the main method of inventory control in the supply chain environment.