Generally, the drying method of soy protein isolate is spray drying instead of freeze drying. Freeze-drying is not the best method to process plant protein products because of the polymerization of disulfide bonds of 7S and 11S proteins under freezing conditions, which reduces the solubility of isolated protein products. There are several forms of spray drying, such as pressure spray, centrifugal spray and two-fluid spray. Pressure spray drying is the best way to produce isolated protein. Although the particles produced by pressure spray drying are small, the isolated protein products have high bulk density. Centrifugal spray drying has low bulk density, and a large number of bubbles are brought into the product after hydration, which will reduce the gel strength of protein, and the shelf life of products with low bulk density is not ideal. When the protein liquid is spray-dried, it is advisable to control the inlet air temperature at 15 ~ 16℃ and the exhaust air temperature at 8 ~ 85℃. If the spray temperature is too high, the NSI value of protein will be reduced, and if the protein powder stays in the spray tower for too long, the gelation and NSI value will also be reduced.