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.