Dynamic modelling method for parallel indexing cam mechanism was presented based on multi-body system dynamics according to the analysis of mechanism feature. Rigid-flexible coupled dynamic model was established by means of Adams, Pro/E and Ansys. Dynamic simulation has been done. It follows the analysis of simulation that modified cosine transmission function is not suitable to be applied in high speed, heavy load or precision transmission cases. The effects of load inertia, input speed, and stroke angle to torsional vibration were illustrated corresponding to dynamics simulation.