Taking Chaohu Lake basin for an example,this paper analyzes the influences of eutrophication factors on chlorophyll a by using structural equation model(SEM).According to the mechanism of lake eutrophication,four intrinsic variables including physical factors,nutrients,organism and phytoplankton are introduced in this model.Along with five eutrophication factors,the SEM-based eutrophication model is established.The results show that the SEM-based model demonstrates the relationship between eutrophication factors and chlorophyll a,and it can directly predict the concentration of chlorophyll a with combination of other methods.