Abstract: Based on the engineering problem that the mechanical properties of weak interlayer are poor and the slope is easy to destroy, the numerical calculation model with weak interlayer is established by FLAC^3D. The influence of thickness, depth and lithology of weak interlayer on the horizontal displacement and safety factor of slope is analyzed. The results show that the increase of the thickness of the weak interlayer, the horizontal displacement increases gradually and reaches 7.44 m, the safety factor of the slope decreases linearly and the minimum safety factor is 1.13. With the increase of the depth of the weak interlayer, the horizontal displacement at the foot of the slope decreases gradually, with the minimum value of 3.71 m and the decrease of 23.88%. The horizontal displacement at the intersection of weak interlayer and slope increases gradually, with a maximum value of 6.90 m, an increase of 35.56%. The slope safety factor decreases from 1.36 to 1.27 and a decrease of 7.09%. With the increase of cohesion of weak interlayer, the horizontal displacement decreases gradually, with a minimum value of 3.45 m, a decrease of 53.06%, and the slope safety factor increases from 1.15 to 1.27, an increase of 10.43%.