The grievous gravitational erosion on Loess Plateau is the major ero- sion type of the region.The paper,with the quantitative geornorpholo- gical method,having analysed the topographical factor in gravitational erosion,raised the concept of topographical factor value,worked out the isograms of regional height facing vacancy for the area and the topogra- phy factor,proposed topographical index of gravitational erosion strength under different combining condition of lithology,it also explores the re- gional nature of gravitational erosion strength.