Lake evaporations of Kangshan, Tanyin, Duchang, Xingzi and Hukou Stations in adjacent Lake Poyang are calculated individually by using instmmental reduction method and climatic model. The mean of the calculated results of the two methods calculations in 5 stations couJd be regarded as the lake evaporation in Lake Poyang. In 1955-2004, the average evaporation of Lake Poyang reached an annual 1081.2 mm and evaporative quantity of 27. 06 ×10⁸ m³. In addition, the trend of yearly and monthly evaporation were analysed, ie. a gradual decrease of evaporation in the past 50 years was noticed except for May, with an annual dropdown of 2.79 mm and a quantity of 0.05 ×10⁸ m³, which could have great impact on the utilization of water resources and aquatic environment in lake districts. Finally, possible reasons are suggested.