Abstract: Effects of petroleum spray oils(PSO)control program (i．e．applying PSO mainly for pests management)and the farmer control program (i．e．applying chemosynthesis pesticides mainly)on the structure and dynamics of pest natural enemies communities in citrus orchard were studied in Huangyan，Zhejiang Province from Aug．1997 to Jun．2000．The results show that the natural enemies communities are more abundant observably and the evenness index of the communities is more stable for PSO control program than for the farmer control program ．The abundance of natural enemies Communities increases year by year for PSO control program ，but the diversity index of the communities is basically uniform．