Aiming at the trajectory tracking problem of nonholonomic wheeled mobile robots in the presence of obstacles in the environment, a velocity space based concurrent obstacle avoidance and trajectory tracking method(VSTTM) is proposed. Firstly, a velocity space is built according to the dynamics of the robot, and the control set made up by velocity pairs is constructed. Then, an objective function is designed to evaluate the controls, among which the tracking error function evaluates the tracking errors, the collision detection function checks if a collision happens, and the terminal-state penalty term guarantees the stability of the proposed algorithm. Finally, the optimal collision-free control is found through an optimization progress. Simulation results show the effectiveness of the proposed approach.