To establish an integrated theoretical model for the evaluation of dynamical reliability of a MEMS cantilever, the mechanical response of the cantilever with tip touch substrate to shock is analyzed. Because the difficulty in describing the dynamical response dealing with touch behavior. This paper presents an approach to convert the dynamical process into models that can be calculated. To solve the equation of motion in forced vibration, the whole process is divided into two parts: motion before the touch and motion after the touch. The beam is treated as cantilever in the first part. In the second part, its one end is fixed and the other end is simply supported, but the two ends have different heights. The height difference is eliminated by a special method. Taking into the continuity of simulation process and influence of the touch, the speed of cantilever at the end of the first part is adjusted into the form that could be accepted by the second part by conversation of energy.