Objective: The paper explores the using characteristics of antitumor drugs after the national centralized volume-based drug procurement policy and provides suggestions for monitoring of antitumor alternative drugs, as well as the optimization of the policy. Methods: Descriptive statistical methods were used to analyze the expenditures, DDDs and DDDc of antitumor drugs before and after the policy using the drug purchasing data from the National Drug Supply Security Information Platform from 2019 to 2020. Results: The expenditures and DDDc of antitumor selected varieties decreased by 31.87% and 51.55%, while the DDDs increased by 40.61%. The overall expenditures and DDDs of antitumor alternative drugs increased by 49.20% and 41.62% respectively, while the DDDc changed in small increments. Among original and generic drugs, the increase of DDDs of selected generic drugs was higher than that of original drugs, and the cost of the two kinds of drugs decreased obviously. The growth rate in expenditures and DDDs of alternative original drugs was higher than that of generic drugs. Among the drugs with different degrees of substitution, the increase of expenditures, DDDs and DDDc of certain degree of substitution drugs was much higher than that of basic substitution drugs. Conclusions: The implementation of the national centralized volume-based drug procurement policy achieved obvious effects in reducing the drug price and saving the cost in antitumor selected varieties, but the substitution effect of selected varieties to alternative varieties was insignificant. Information technology should be used to monitor the limit of expenditures and dosage of higher degree of substitution varieties, and to accelerate the substitution of expensive original drugs by generic drugs passed the consistency evaluation.