Abstract: In order to study the influence of downward mining along the slope on the slope stability, based on the mining subsidence theory in this paper, the effect of mining on the sliding surface was analyzed by using UDEC numerical simulation software. The influence of the deformation of the sliding surface on slope stability under different mining height (including 0.8 m, 1.2 m, 1.8 m, 2.4 m, respectively) was simulated by utilizing the test bed with a variable sliding surface. The results show that downward mining along the slope makes the upper sliding surface occur an S-shaped deflection. Cracks of different degrees will appear in the slope body. And with the increase of mining height, the deflection degree of sliding surface increases; cracks in the slope body are widened, and the whole stability of slope body reduces drastically.