Micro-electromechanical system has been used for a wide application in various engineering practices. However, failure related to damage of such a system often comes about during this extensive application of the system under complicated operating conditions. This work studied the post-buckling behavior of an elastic micro-plate under in-plane compressive loads. Based on modified couple stress theory and the Talreja’s tensor-valued internal state damage model, a novel model considering size effect and damage effect is developed for this work. The nonlinear governing equations of the micro-plate were derived by applying principle of minimum potential energy and solved via finite difference method and iteration method. The damage evolution law is employed to model damage accumulation while the post-buckling equilibrium path is simultaneously predicted. The effects of material length scale parameter, initial geometric deflection, aspect ratio, thick-span ratio, as well as damage on the post-buckling behaviors of the micro-plate are discussed in detail.