Abstract: Ambient water quality criteria are the important basis for establishing water quality standards, and the significant part of scientific water quality management system. The Dianshan Lake is an important water resource located in the upstream of the Huangpu River. Its water quality directly affects the quality of the drinking water in Shanghai. Since the first algal bloom in 1985, the ecosystem in 1985—1992 is not a healthy but relatively stable compared with that other periods. To protect the lake and fulfill its designated uses, this research developed a water quality criteria based on the change of Chl.a in the recent 23 years. On inter-annual variation the concentration of Chl.a in the lake can be divided into four periods: relatively stable, slow rise, rapid increase and slow down. Analysis by the temporal reference state and the frequency distribution methods suggested that Chl.a should be divided into winter-spring and summer-autumn on season variation. The recommended criteria value of Chl.a in winter-spring time and summer-autumn time were 2.0 μg/L and 5.0 μg/L, respectively, which were validated using the input-response relationship referring to the TP criteria of Taihu lake.