Abstract：Location of critical failure surface and identification of its parameters are two very important problems in slope stability analysis. At first，location of critical failure surface is studied. Here，the coordinates of some reference points are taken as searching objectives，so the problem of location of critical failure surface is transformed to a typical complicated optimization problem that can not be solved by traditional optimization methods. To solve this problem，the new global optimization method that is called bionics algorithm-immunized evolutionary programming is introduced. So，taking the coordinate of reference points as optimization parameters and safety factor as optimization objective，a new method to search critical failure surface is proposed. At last，through a typical numerical example and an engineering example，this new method is verified. The results show that this new method can solve the problem of location of critical failure surface very well and can be applied to engineering practice. But only to locate the critical failure surface with supposed parameters can not get the suitable safety factor of slope，the better way is to search the critical failure surface and its parameters at the same time. This problem can be solved in the second part of this paper.
