Abstract: The deformation and instability laws of the slope in Heidaigou Open-pit Mine are studied by using the similar simulation experiment. The results show that with the development of open-pit excavation, the slope rock mass is first deformed and destroyed at the top step of the slope, and the main deformation mode is the slight movement to the side slope surface, and the slope will not slip; continue to increase the mining step, the middle step of the slope is affected by the squeeze from the rock mass below, and the step after the upper excavation gradually rises up, which is basically similar to the actual project, and no slip will occur; under the continuous open-pit mining, the displacement in the vertical direction is always larger than the horizontal direction. It can be seen that the slope step is affected by mining disturbance, and the step is torsional deformation, and the bottom step gradually bulges with the end of excavation.