MEMS (Micro Electro Mechanical System) devices are fabricated with microfabrication method, and contain mechanical and electric behavior. Therefore, it is important to analyze an interaction between the two behavior. As a result, equivalent circuit method, which enables to analyze whole system at a time, is expected to become a key to that. However its models and analysis methods in previous way are inapplicable to nonlinear region. This research is intended to apply equivalent circuit method to nonlinear region. I developed two nonlinear models: one shows hard spring effect comes from clamped-clamped beam and another shows soft spring effect comes from comb shaped electrode.