Because Jiangnan can't supply the food that Beijing needs in time. According to historical records, Chang 'an, the capital of the Tang Dynasty, was supplied by Jiangnan. Due to "the waterway is too crowded, and the ship blocks the pass", "less travel is more delayed", and the sailors in the south of the Yangtze River are unfamiliar with the Yellow River, and the water transportation mode was backward at that time, the annual transportation volume was far from meeting the demand of Beijing, and even the normal supply could not be guaranteed, which was even worse than natural disasters. In order to speed up the water transportation and solve the food and material problems faced by the imperial court, Pei Yaoqing put forward the idea of placing warehouses along the river in combination with his own experience and geographical conditions at that time.