In China, the farming-pastoral zone of northern China has become one of the academic research hot spots. Xiliaohe watershed is a part of the farming-pastoral zone of northern China, located in the east of Three North Area of China. Horqin sandy land is in this watershed, which is well known as the biggest sandy in China. Xiliaohe watershed’s weather is meteorological drought with less rain. And the evapotranspiration is strong. The situation of water shortage is serious. Water shortage has become the bottleneck to the development of local in dustry and agriculture. Also, Xiliaohe watershed is considered as a vulnerable eco-region because of water shortage. Potential evapotranspiration, seen as the basis for the actual evapotranspiration research, is important not only to the water resources research but also to the study of the relationship between vegetation and mois ture. This study aims at analyzing the spatial-temporal pattern of potential evapotranspiration in the Xiliaohe watershed. Based on the(limatic data from 45 meteorological stations throughout the Xiliaohe watershed during 1974 and 2005, potential evapotranspirations (E_T0) are calculated using the CI method (Calculate first, Interpo late later). Firstly, potential evapotranspirations of 45 meteorological stations are calculated using the Penman Monteith (98) Model recommended by FAO. Secondly, based on the ArcGIS 9.0 software, using the Ordinary Kriging method, potential evapotranspirations in Xiliaohe watershed are interpolated month by month. Conclu signs are as follows: 1) E_T0 is positively related to temperature, sunshine hours and wind speed but inversely related to average relative humidity. 2) Affected by the impact of various meteorological elements, the monthly E_T0 change curve is a single peak curve. E_T0 is always lower in winter and higher in summer, the end of spring and the beginning of autumn. 3) The spatial distributional trend of potential evapotranspirations in Xiliaohe water shed is that E_T0 decreases gradually from the Horqin sandy land (the middle of the Xiliaohe watershed) to the northeastern side and southwestern side.