Objective:To analyze dimension quantity structure-activity relationship (2D-QSAR) of 7,9,10 and 11 sites substituted analogues of camptothecin and explore the mechanism of camptothecin analogues inhibitting enzyme. Methods:First preselected the parameters and then modeled the equation using PLS method. Results:A correlative equation was obtained and the predictive ability of the resulting equation had been successfully tested by 5 comptothecin analogues. Conclusion:Depending on the QSAR results and SAR conclusions, the interaction pattern between camptothcin analogues and ToPo Ⅰ is better understood and provides a base for the reliable drug design.