The virtual operation for MEMS device is a key issue in the design and simulation of MEMS system. Compared with traditional finite element method, we put forward a method of dynamic analysis base on separated time and space. For accelerometer's cantilever dynamic analysis, the movement process of cantilever is the result of the law of movement multiplied by the steady state value of cantilever. Comparing with the result of dynamic analysis of cantilever used by ANSYS, it has confirmed the validity of method of separated time and space for dynamic analysis.