Abstract: A new method of deformational analysis was adopted to carry out the three-dimensional stability analysis of a slope so as to accord with the actual destruction pattern as possible. In the method, the residual thrust method and the principle of optimality were used to construct the critical slip field (CSF) of the slope, which not only is convenient to find out the arbitrary shape of critical slip surface, but also can be used in optimum design at a given safety factor by using the counter-analysis method. Corresponding software was compiled to calculate a mining engineering project, the calculation results agreed with the measured data, and some optimum design schemes were proposed for the engineering project.