Abstract: Aiming at the problem of large dynamic overshoot under traditional proportional integral(PI) control, the most commonly used frequency conversion-phase shift method for full-bridge LLC resonant converters, a PI-sliding mode hybrid control method is proposed. This control method combines the advantages of PI control and sliding mode control, using sliding mode control when the output voltage is far from the reference voltage, switching to PI control when the output voltage is close to the reference voltage, and completing the smooth transition between the two through fuzzy control. The working principle and working characteristics of the full-bridge LLC resonant converter in frequency conversion mode and phase shift mode are analyzed in detail, and the specific implementation scheme of the hybrid control method is given. In order to verify the feasibility of the proposed method, the simulation model is built and the performance comparison analysis of PI control method, sliding mode control method and PI-sliding mode hybrid control method is carried out. And made a prototype with a rated power of 2 kW. The experimental results indicate that the proposed PI-sliding mode hybrid control method can remarkably lower the system's dynamic response overshoot, and eliminate the chattering issue in the steady state stage, demonstrating a good control performance.