Abstract: The discrete mechanics and optimal control (DMOC) is a recently developed effective method to solve the optimization control problem. However, the original DMOC usually leads to some numerical oscillation of the control forces, which is unfavorable for the control output. In this paper, the causes of the numerical oscillation are analyzed. Then a feasible solution by introducing a gradient penalty term to the objective function is proposed. Finally, numerical examples validate the effectiveness of the proposed method. The simulation results show that the improved algorithm can ensure smoothness of the control forces under the condition of the minimization of the total control forces.