Based on the eutrophication appeared in Chaohu Lake, we analyzed the relation between the multifactor coupling and chlorophyll-a (Chla) with monitor data from 2005 to 2009 in western lake, and by correlation analysis and stepwise multiple regression, we inferred the dominant factors of algal blooms and established the prediction model of Chla variation. The results indicated that seasonal trend of Chla concentration was greater in summer and lower in winter in western lake. The Chla biomass was influenced by multiple effects of environmental factors, in which the dominant ones were air temperature, water level and COD_Mn. Under multifactor coupling environment, meteorologic and hydrologic factors were most significant to algal blooms. These results might provide scientific foundations for prediction and control of harmful algal blooms in Chaohu Lake.