Abstract: To deal with the vibration brought by the non-rigid characteristics of the leg mechanism during the humanoid robot walking, a walking vibration suppression method is proposed based on optimal control. Firstly, the vibration is modeled, and then the model is added to the original dynamics model of the robot. Then, the preview control method is used to generate a control trajectory subjected to the COM (center of mass) acceleration constraints based on the extended dynamics model, where the trajectory serves as the initial solution of the optimal control problem. And starting from this initial solution, the constrained optimal control problem is solved by iteration method, yielding an optimal control trajectory which suppresses the vibration in a feed forward manner. Finally, contrast walking experiments of the preview control method and the proposed method are performed on the humanoid robot Kong. The experimental results show that the proposed method significantly reduces the oscillation of the ZMP (zero momentum point) and the shaking of the torso during the walking process of the robot. The effectiveness of the method for walking vibration suppression is validated.