In the water source areas of Beijing City and Tianjin City,ecological environment is highly fragile,and soil and water loss often exhibits strong spatial variability and occurs unpredictably.Along with data of climate,soil,terrain,land use and vegetation coverage,soil erosion and its spatial differentiation were studied based on the revised universal soil loss equation (RUSLE)model and geographic information system (GIS),in Xibeigou watershed of Luanping County,Hebei Province.The results show that the annual average rate of soil erosion was3816.835t/(km ²·a),classified as middle-grade erosion.Annual average of potential soil erosion was 31583.15t/(km²·a),about 8.28 times of the former.Meanwhile,soil loss was obviously spatially differentiated.Among different land uses,sporadically distributed farmlands with steep slopes had the strongest soil erosion intensity,and next to it was highly weathered and degraded grassland's,which accounts for 59.38% of the total area of the watershed and 88.48% of the total sediment as the main source of the soil loss.With the increasing slope,the soil erosion intensity increased markedly.Approximately one third of the total area of this region has a slope degree higher than 25°,while this proportion contributed two third of soil loss.Soil losses also differed among lands of various aspects,as in order of sunny slope>half-sunny slope>half-shady slope>shady slope>flatland.