Abstract：In traditional landslide stability analysis，the shape and position of slip surface depend on drilling investigation and engineering experience to some extent. Especially，the complicated landslides are found with potential multi-shear outlets and multi-slip surfaces；and mistakes and leaks are usually encountered when estimating the slip surface，thus the results will lead to the failure of landslide treatment. The strength reduction FEM is an effective method to study landslides slip surface for it can automatically find out the accurate critical slip surfaces and corresponding safety factors；and the numerical non-convergence occurs simultaneously through the parameters reduction of soils of landslides. Moreover，it can still find out the glide order of each slip surface. By restraining shear outlets successively，a landslide is studied to find out all slip surfaces and shear outlets accurately in which safety factors are lower than the ones calculated by strength reduction FEM. The proposed method overcomes the deficiencies of traditional methods in determining complicated landslide slip surfaces；and it can provide basis for the projects of landslide treatment.
