Analyzing the time series of the whole Northern China and the sub-regions of it,Northeastern China,northern China,the east part and the west one of Northwestern China,it is found that the pan evaporation obviously decrease in the past 45 years(1961-2004).And the space pattern of change is: Pan evaporation declined least in the Northeast China,when moving westward,its decrease trend gradually increase.Analysis of the relations among pan evaporation and some environment factors,for instance,wind speed,precipitation,relative humidity and diurnal temperature range,etc,show that either whole North China or in its sub-regions both the diurnal temperature range and wind speed were the most important factors,while precipitation,relative humidity and temperature,etc,were also important impact factors on pan evaporation.In total,many meteorology factors have a close correlation with pan evaporation.The correlation changes with the change of time and space in the past 45 years,the influences of the diurnal temperature range and wind speed changes on pan evaporation change were dominant,they are the primary reasons for the decreasing of pan evaporation in the Northern China in the past 45 years.