Based on the data of NOAA/AVHRR and the monthly monitoring data in 2002 -2007,the spatial and temporal variation of algal blooms in Lake Chaohu was analyzed.Meanwhile,the relationships between the chlorophyl ( Chl - a) contentin algae and the total nitrogen (TN) and total phosphorus (TP) concentrations in water bodies of Lake Chaohu were studied.The results showed that the relationships between Chl - a content and TN and TP concentrations were quite different in the monitoring zones.The algal blooms occurred in the western area of the lake,where Chl - a content was above 20 μg/L all the year,and achieved the peak value 77.87 μg/L in August.No algal blooms occurred in the eastern area of the lake,with Chl -a content below 5.5 μg/L all the year.In the eastern area of the lake,Chl -a content had positive correlations with TN and TP concentrations,and increased very fast when the TP concentration was above 0.15 mg/L.The Chl -a content increased with increasing TN and TP concentrations when they were below 5.8 and 0.2 mg/L in the western area of the lake,but decreased with increasing TN and TP concentrations when they were 5.8 ～ 9.4 and 0.2 ～ 0.3 mg/L respectively,and increased with increasing TP concentrations when it was above 0.3 mg/L.To reduce eutrophication,the focus of management must be on decreasing inputs of phosphorus and internal phosphorus inthe western area of the lake.