Abstract: Based on the red clay slope in the northern part of Pingshuo East Open-pit Mine, the mechanism of red clay slope instability under the influence of goaf is studied. The arch effect, stress distribution and failure rule of red clay slope under the influence of goaf are revealed by numerical simulation analysis and limit equilibrium theory. The results show that the stability of red clay slope has a “step-like” development and change law from stability to failure, and the failure mechanism is “shear-tension crack-slip-collapse” .