Analysis of the climatic characterization of potential evapotranspiration (ETp) is significant for understanding the impact of climate change on water cycle.This paper estimates the ETp of Beijing station based on Penman-Monteith method.The ETp shows significant increasing trend during 1951-2009.The non-dimensional sensitivity coefficient was employed to identify the sensitivity of ETp to key climate variables.The results show that relative humidity is the most sensitivity factor, followed by air temperature and solar radiation.