A high-fidelity dynamic model of an electrostatically actuated microswitch is developed for the performance assessment of a membrane-type MEMS switch. The simulation model accounts for multi-physics behaviors involved in the switching action such as structural dynamics, ambient damping mechanisms, and electromechanical coupling effect. The genuine attribute of the present model is accounting contact-bouncing motion between moving switch and a stationary electrode foundation, which takes place before permanent contact is achieved. To do this, a localized Lagrange multiplier method is utilized in nonlinear governing dynamic equation. The simulation model can be used as design tools to improve switch performance such as switching time and actuation energy and reduce switch bounce in future designs.