Abstract: Presently, the damping injection of passivity-based controller of Buck converter can’t make converter acquire excellent performance. Aiming at this problem, an approach is proposed which can be used to calculate and optimize damping injection in the paper. Firstly, the transfer function of the Buck converter system based on passivity-based controller is established, the output current and its overshoot of the system is found when input is step, and finally the range of value of the damping injection is decided by correcting overshoot of the output current response. The damping injection is optimized by using genetic algorithm and the optimal damping injection is obtained. The Buck converter can get excellent performance due to passivity-based controller based on optimal damping injection. The simulation results prove the feasibility of the passivity-based control based on optimal damping injection proposed in this paper.