OBJECTIVE To investigate the factors influencing the changes in purchasing quantity in the procurement varieties of the first batch of volume-based drug centralized procurement （hereinafter referred to as centralized procurement）. METHODS Using 25 procurement varieties of the “4+7” policy as research objects， the changes in purchasing quantity of procurement varieties were analyzed before and after the implementation of the “4+7” pilot， renewal and expansion policies. The influential factors were determined from the three levels of drugs， medical institutions and regions； and the multiple linear regression model was used to analyze the influential factors for the changes in the purchasing quantity of procurement varieties. RESULTS Before and after the implementation of the “4+7” pilot， renewal and expansion policies， the purchasing quantity increased by 52.1， －0.2， 85.8 ten thousand DDDs on average， compared with base period. During pilot， renewal and expansion period， DDDc decrease in procurement varieties was positively correlated with the increase in purchasing quantity （P＜0.01）. During the pilot and renewal period， the number of absolutely alternative varieties was positively correlated with the increase in purchasing quantity （P＜0.1）. During the pilot and expansion period， the number of alternative varieties to a certain extent was negatively correlated with the increase in purchasing quantity （P＜0.05）. During the renewal period， the increment of purchasing quantity in tertiary hospitals was smaller than that of primary medical institutions （P＜0.05）. CONCLUSIONS There is a relationship between the decline of DDDc and the changes in the purchasing quantity， that is， the more the drug price dropped， the more the purchasing quantity increased. The number of alternative varieties for centralized procurement will affect the changes in their purchasing quantity， but it is not always stable. With the implementation of the policy， the volume of primary medical institutions gradually exceeds that of tertiary institutions， indicating that the consumption of centralized purchased varieties is transferred to the primary medical institutions， and centralized procurement has promoted the implementation of the hierarchical diagnosis and treatment system.