Based on the monthly pan evaporation data of 5 meteorological stations over the Dianchi Lake basin from 1961 to 2010，the temporalspatial distributions of pan evaporation, and the correlations between the pan evaporation and the dynamical factor (wind speed), thermal factors (average temperature, average temperature diurnal range, and sunshine duration), the water factors (precipitation, relative humidity, and vapor pressure) and other factor (total cloud cover) are analyzed.The contrast of the annual variations of pan evaporation between the Chuxiong meteorological station and the Dianchi Lake basin during the same time is conducted. The results indicate that mainly 2 to 4 year period cycles can be detected in the annual variation of pan evaporation. In the recent 50 years，not only the annual pan evaporation, but also pan evaporation in spring and in summer showed a clearly downward trend in the Dianchi Lake basin. The downward trends of pan evaporation in the middle and north parts of the basin were more obvious than those in the south part of the basin and areas surrounding Kunming Station. The changes of annual, spring, autumn, and winter pan evaporation were basically similar in the Dianchi Lake basin and Chuxiong Station, but the changes of pan evaporations in summer were greatly different in the two areas. Correlation analysis between pan evaporation and meteorological factors shows that the trend of pan evaporation variation in the Dianchi lake basin was positively correlated with the heat factor and dynamic factor, and negatively correlated with water factor and total cloud cover. The effects of average temperature diurnal range， sunshine duration， vapor pressure, and wind speed were remarkable.