In the research of non-point pollution,how to calculate soil erosion modulus is a very important step. With the technical support of GIS,the universal soil loss equation (USLE)was used to calculate the soil erosion modulus of Changshan region in the watershed of Songhua lake. Topography,vegetation and precipitation that influence the soil erosion mould were considered. The relationships among those factors were discussed and some control measures were proposed based on the results.