Abstract: During or after cutting of natural slopes,different gradients of slopes are usually formed on the upper part and the lower part.According to results of centrifuge model tests and in-situ tests,there are two failure patterns of the slopes.One is the failure plane starting at the top of the slopes,and the other is the failure plane starting on the surface of the slopes.The critical depth of the two failure patterns were calculated by use of the upper-bound theory.Through comparison between the two critical depths under same conditions,the conditions for occurrence of the two failure patterns were discussed and defined.Then the critical depth,safety factor in case of the excavation depth less than the critical depth and the soil pressure in case of the excavation depth larger than the critical depth were given.These results were meaningful to the design of slope cutting.