Abstract: In the course of ore mining, there is often a situation of combined underground and open pit minings. According to the relation between spatial positions of stopes, parts the influenced realms by different mining excavations are overlapping. It results in the interaction and superimposition of two kinds of mining effect and hence forms a composite dynamic system. Thus, the deformation mechanism of slope rockmass becomes more complicated and differs from that caused only by open pit mining. However, in treatment of the conventional method for slope stability, this kind of influence is usually used. Its result was different from the real situation. Therefore, in this paper an evaluating method is derived on the basis of theoretical analysis and case study. It provides scientific basis for design and safe production of these mines with continuous excavation.