At present, the conventional flexible DC transmission converters mainly track the internal energy through sliding mode control or PI control. Due to the lack of dynamic adjustment of controller parameters, the control effect is poor. For this reason, a passive control technology for flexible DC transmission converters based on an improved ant lion algorithm is proposed. The passive controller is designed by constructing the energy storage function. The ant lion algorithm is used to dynamically solve the optimal parameters of the passive controller, and the control process is optimized by adjusting the transition time and overshoot. In the experiment, the control performance of the designed passive control method is tested. The final results can prove that the proposed method has a fast convergence speed of energy function and an ideal passive control effect when it is used to control the transmission converter.