Abstract: Based on the daily pan evaporation data from 1961 to 2000 in Alar weather station, the characteristics and trends of the seasonal, annual and inter-decadal changes were analyzed in Alar irrigated area. The results indicate that evaporation is the decreasing trend in recent 40 years with -78.68 mm/10 a. And monthly evaporation is also the decreasing trend. Compared to that in cold period, the decrease of evaporation in warm period is obvious.