Abstract: The concept of critical slip field (CSF) and the method of its numerical simulation are put forth in the paper. CSF is the field of maximal residual thrust curves in a slope under critical condition, composed of numerous hazardous slip surfaces which do not intersect each other. The shape of these surfaces is not defined mathematically, and among them is the critical slip surface. The results of some examples demonstrate that the critical slip surface in CSF is a numerical approximation to theoretical solution .Furthermore,it is even peculiar to evaluate slope stability with CSF itself.