Abstract: The water surface evaporation in Bosten Lake used in the past the est－ imating value calculated through the data or formula of the other parts of the area，so that no on－the－spot data can argue its accuracy．This article based on the on－the－spot survey data beginning from April 1984 analyses the water surface evaporation rule in Bosten Lake；through the on－the－spot survey data in the Hong－sha－liang peninsula of southern Lake obtains K₁ （ E601/p20CM ），by the evaporation observation of 3000 mu of piscina requires K₂ （piscine／E601），and through the temperature measure deter－ mines provisionally K₃(0.99) ，lastly gets the Lake surface evaporation as following：E=K₂·K₂·K₃·E₀E₀-ϕ20 CM evaporation.