For three-wheeled omni-directional mobile robots that slipping is almost inherently encountered in motion,one suitable trajectory tracking control system based on a improved dynamical model with slip is proposed based,which gives more accurate control result. The kinematics model and dynamics model for omni-directional mobile robots are built. By analyzing the wheel contact friction forces both in the wheel hub rolling direction and in the roller rolling direction,an amendatory dynamics model is presented. This model is introduced into the closed trajectory tracking control system to solve the trajectory tracking problem. The simulation of trajectory tracking control system is carried out on the platform of Matlab/Simulink. The results indicate that the trajectory tracking control system of three-wheeled omni-directional mobile robots based on the improved dynamical model with slip has good stability and accuracy.