Abstract: Based on the existing key strata theory, the concept of “the key strata” which controls the open-underground mining slope stability was proposed, taking open-underground mining in Pingshuo Mining Area as an example, the deformation and failure regularity and the regularity of strata movement about the slope of open-underground mining was studied, the theoretical analysis results are verified by the physical simulation and numerical analysis method. The results showed that under the coupling action of “the key strata”, the slope mainly shows that two kinds of deformation and failure modes which are settlement of sliding failure and potential sliding failure, the stability of open-underground mining slope depends on the counterbalance between the slip power provided by the critical hard rock and the sliding resistance provided by the weak layer, and the physical simulation, the results of numerical analysis and theoretical research results have obvious consistency.