In recent years, in view of the absence of kinematics analysis function of mechanisms in the virtual assembly system, the method of kinematics analysis of mechanisms based on dynamics of multibody systems in virtual assembly environment is presented. A mechanism is considered as a multibody system and the kinematics equations are established based on Descartes coordinate system. All the kinematics parameters, just like position, speed and acceleration, can be obtained through solving the kinematics equations. In addition, the realization method of mechanism motion simulation in virtual assembly system is also proposed which contains the hiberarchy, data structure, module classes and simulation process of the system. The method is implemented and validated based on the prototype system VAPP(Virtual Assembly Process Planning).