Based on the idea of life table, the concept and index of insect pests accumulated damage amount were described and the damage degree and its fluctuation were compared. Through analyzing the deterrent effect of azadirachtin on the adults of striped flea beetle (SFB), Phyllotreta striolata (F.), the results showed that the control mechanism was its strongly deterrent effect. When 0.5 ml.L-1 azadirachtin was applied, 83.75% of the SFB adults was kept away from the host plant. The population trend index (I-value) of SFB decreased from 3.8680 in the control to 0.3354. The interference index of population control (IIPC) was 0.0863 at this dosage. The results come from the fields, which avoided the space limit of laboratory experiment, were the main basis to evaluate the deterrent of allogenetic plant secondary substances to insect pests. Such index provided an objective method to assess the pest damage degree, and would play an important role in the dynamic researches of pest ecological control.