Erhai Lake is the second largest freshwater lake in Yunnan Province.As the primary producer of the lake,phytoplankton plays an important role in the status of the lake.Through the investigation and analysis of algae composition in 12 months in Erhai Lake,it is found that algae in Erhai Lake are mainly composed of chlorophyta,Diatom and cyanophyta,among which Microcystis of cyanophyta and Phlebothrix of Diatom are the dominant genera throughout the year.The abundance and biomass of algae varied significantly with time and space,especially in autumn and the southern region.This spatial and temporal variation was related to various environmental factors such as seasons,surface runoff and population distribution.The growth conditions of algae and the phenomenon of blooms after overgrowth were analyzed in detail,and then a detailed reproduction plan was put forward for the recovery of algae in Erhai Lake.This provides a scientific basis for further understanding of Erhai lake ecosystem and implementing lake protection and management.