Abstract: For the slope engineering of large open pit mine, the current situation and mechanism of landslide are analyzed. 3D geological model of the slope is established. Then, the analysis and evaluation of slope stability are carried out with strength reduction method and limit equilibrium method. The height of step and angle of slope are optimized. The results show that the displacement of sand soil on the top of the working slope is much larger. The factor of safety was equal to 1.4, which showed that the slope was stable overall. But the local landslide was possible in the three upper steps, which was manifested as arc-type landslide or collapse. The structural surface of non-working slope was kaolin layer on the toe of slope, and the displacement of kaolin soil layer was larger. In addition, the surface heavy load increasing the sliding trend, the landslide was aggravated. The factor of safety was equal to 0.9, which showed that the slope had slid. The landslide was manifested as arc-type and bedding, which was accordance with the filed landslide. The height of the step of mudstone, sand soil and clay soil is suggested to be less than 6 m, and that of siltstone can reach to 10 m. When the slope angle is 23°, the safety factor is between 1.3 and 1.5, which can meet the specification requirement.