In order to understand the status of phytoplankton community in the Dishui Lake and its relationship with water quality,8 sampling sites were investigated monthly from January to December in 2011 ,including the lake's center,sea sluice and water inlets. A total of 61 genera and 128 species of phytoplankton were identified,among which, above 70% are Bacillariophyta and Chlorophyta. The dominant species of the year were Chroomonas acuta, Chlorella vulgaris, and Chamydomonas snowiae. There were most domi nant species in March,April and Novermber,which indicated that the community structure might be more complicated in spring and autumn than that in the other 2 seasons. Shannon Wiener Index(H' ), Margalef index (d) and Pielou Evenness Index(J) were 1.23±0.46,3.97±0.66,0.83±0.29 respectively. The di versity index showed that most of the samplings were in the status of light and moderate pollution. All of the 3 index were higher in spring and autumn. One way analysis of variance demonstrated that both of phytoplankton species and quantities had an extremely significant difference among months, while no significant difference among the sampling sites. The total phytoplankton density was 7.42 ×10^6 ind./L, and had a strong relevance with water temperature. Canonical correspondence analysis (CCA) showed that, the densities of main phytoplankton species of the Dishui Lake were greatly affected by TP and pH, besides water temperature.