Abstract: The universal soil loss equation (USLE) and revised USLE (RUSLE) are often used to estimate soil erosion at regional landscape scales, however the method of extracting the topography (LS) factor is the main limiting factor . The principles, methods, processes for extracting topography factor from watershed scale were discussed based on slope hydrology and soil erosion. With the consideration of the flow divergence and convergence, sedimentation, channels conditions, an estimation method for topography factor was proposed based on multiple flow direction algorithm and GIS. A tool named LS-TOOL was designed for calculating. Comparing with the two methodologies of AML(ARC Macro Language)and C++), LS_TOOL delivers improved the LS factor. The results showed that results calculated by LS_TOOL was more closely with the reality of the Xiannangou catchment than results by AML and C++ in spatial pattern, and LS_TOOL was more efficient than AML and a little bit lower efficient than C++. This research indicated the LS_TOOL can automatically calculate topography factor for watershed and regional scale.