Abstract: Slope critical sliding field algorithm is a new method in slope stability analysis. It can quickly and accurately determine the arbitrary shape of critical sliding surface of multi-layer and multi-step slopes, and give an overall evaluation of the global and local stability of slope. This paper firstly uses the critical sliding field algorithm to probe the sliding surface of Longqiao waste-dump slope with the original design of 15 slope angle. The global safety factor of slope is found to be 1.42. The results show that the original design of 15 slope angle is too conservative. Then the expending method of the critical sliding field algorithm is used to carry out the reverse analysis. Given safety factor of 1.30, the optimum slope angle is found to be 17. The results can be used to supervise the future dumping work of mines.