Generally, there are two types of critical failure surface of slope, which are circular surface and non-circular surface. To circular slip surface, the search of slip surface can be transformed to search of coordinates of the circle center and radius. While to non-circular slip surface, the search of slip surface can be transformed to search of coordinates of some reference points on slip surface. So, the search on slip surface of slope is a very typical optimization problem. To solve this problem, one new optimization algorithm-continuous ant colony algorithm is introduced. At last, through a typical numerical example, this new method is verified.