A new method to search three-dimensional(3D) critical slip surface for slopes is proposed based on the finite element method (FEM). The FEM is used to analyze the stress field for slopes and calculate the safety factor of 3D potential slip surfaces from the stress results. The genetic algorithm is adopted to search for the most dangerous slip surface and identify its safety factor as the safety margin of slopes. The advantage is that this method can work dependent on one time finite element calculation and without given slip surface. Moreover

it is suitable for 3D complex topography and geological structures. The method feasibility and the code reliability are verified by an example; its practical application is illustrated by a slope example in the reservoir area of Dagangshan hydropower station.