This paper briefly introduces the application of 3S(GIS,RS and GPS) technologies in the dynamic monitoring of soil erosion in the source area of the Danjiangkon reservoir.It starts from an introduction of the technical features of 3S technologies,followed by a detailed explanation for the 10 steps on how to proceed with the task,i.e.,data collection,vectorization of contour maps,spatial analysis of vector data,geometric correction of remote sensing images,spectrum sampling of images,interpretation,computation of soil loss intensity,field verification of the outputs,database integration and user interface development.Finally,the paper illustrates the real application of this achievement,as well as the advantages of the 3S technologies for soil and water loss monitoring.