The spatial and seasonal variations of environmental factors and phytoplankton community in Lake Dianchi was investigated. The statistical analysis found that a total of 84 phytoplankton taxon, belonging to 49 genera 6 phyla were identified, of which Chlorophyte were the most abundant, accounting for 59.2%, followed by Cyanophyta, accounting for 16.67% and diatom accounting for 5.95%. The trend of seasonal variation of algae density and biomass was not the same, which was caused by the biomass differences of various species. The Shannon Wiener index (H) was very small throughout the year, and seasonal variation was not significant. Algae density and biomass were positively correlated with total phosphorus (TP), and negatively correlated with nitrate (NO3-) and nitrogen phosphorus ratio (N:P). H was positively correlated with NO3- and N:P, while negatively correlated with TP. Nutrients had great influences on the density and biomass distributions of various taxa of phytoplankton community. The density and biomass of the most dominant species Microcystis sp. had the same relationships with the environmental factors, which were positively correlated with pH, TP and ammonia (NH4+), and negatively correlated with NO3-, N:P, total nitrogen (TN), dissolved organic carbon (DOC) and total organic carbon (TOC). Some biological factors may cause stronger effects on density and biomass distribution of chlorella and diatom, such as interspecific competition and predation, covering the influences of environmental factors.