Based on the data of 20cm pan evaporation and its impact factors over Lake Qingbai basin from 1961 to 2007, the trend was analyzed through Mann-Kendall nonparametric test methods and grey incidence analysis. The main results were as follows; Sig-nificant negative trend of pan evaporation Lake Qinghai basin was detected, with the decrease rate of 4. 47mm per annum, and except for autumn, all season had the negative trends, with the decrease rate from 0. 55 to 1. 83mm per annum, especially in spring, then summer, while winter decrease was tiny. Decreases of the hours of sunshine that mainly caused the decrease of pan evaporation, have resulted into decreases of the diurnal temperature range and the average vapor pressure deficit.