In the present study we evaluated the trophic status of West Lake on basis of investigations from January of 2007 to October of 2010.According to the data associated with species composition,dominant species,density and diversity of rotifers,the relationships between rotifer community structure and eutrophication were evaluated.The result indicated that the water in West Lake had been in a state of eutrophication.The dominant rotifer species were Brachionus angularis and Keratella cochlearis in all 29 species.The amount and diversity of rotifer species are all low.Structures of rotifer community were different in seasons,years and locations.The correlation analysis showed that rotifer density was significantly correlated with water temperature,status of eutrophication, total nitrogen,SD,COD_Mn and pH,respectively.There were significant correlations between Shannon-Wiener diversity index and environmental factors,but only total-nitrogen had obvious correlation with Margalef diversity index.The study showed that there existed an ecological gradient of the community structure of rotifers between intake and outlet,which were influenced by hydrodynamics of water diversion system.