Bosten Lake isone of the biggest freshwater lakes in China.On the basis of in situ hy drological and hy dro-chemical data of Bosten Lake, this paper discusses the annual and seasonal change of water saltof Bosten Lake in detail.During the past 40 years or so, The lake water has undergone an annual changing process and the seasonal change is closely related to the water discharge coming from Kaidu River thatis the largest water source supplying for the Bosten Lake.The farmland drainage contains salt around the Lake.The change of mineralized deg ree in the lake is negatively correlated with the water levelin the pasr 40 years, i.e.when the water levelis lower, the lake mineralized deg ree is higher.With the increase of ion content, Ca²⁺ and Mg²⁺ increase slow ly, while the contents of SO₄^2-, Cl^-and K⁺+Na⁺ show markable increase.The descending ion contentorder is SO₄^2->Cl^->HCO₃->K⁺+Na⁺ >Mg²⁺ > Ca²⁺ >CO₃^2-, and its proportion may differ with the sampling positions in the lake.The hydro-chemical ty pe is SO₄^Na.The lake water sources and lake water circulation are the main factors that have impacts on the change of lake water quality.The measurement for improving Bosten lake water eco-environment are suggested as follows:farmland irrigation quota should be reduced, river water amount flowing into Bosten Lake be promised, the groundwater resources utilization in the Yanji Basin be sped-up, and the lake water circulation intensity streng thened.