An improved sliding mode active disturbance rejection control strategy based on the quasi-continuous algorithm was proposed by utilizing the virtual synchronous generator (VSG) technology to address the issue that the traditional linear control strategy of photovoltaic hybrid power conversion system (PV-HPCS) was difficult to achieve ideal control effect in terms of power and voltage fluctuation suppression, and to improve the performance of PV-HPCS, to stabilize the power fluctuation of the grid and maintain the stability of bus voltage. The VSG was integrated with the dual closed-loop control strategy of voltage and current. The PI control was adopted in the voltage outer loop to provide reference values for the current inner loop. A high-order super-twisting sliding mode observer (HO-STSMO) which realized higher response speed and tracking accuracy was adopted in the current inner loop. The quasi-continuous integral terminal sliding mode controller (QC-ITSMC) was introduced in the form of dual sliding mode switching control law, and an improved exponential reaching law was designed to smooth the system control signal and improve the robustness of the system. The simulation model and experimental platform were built, and the experimental results showed that the improved control strategy effectively suppressed the power fluctuation of the grid and improved the stability of the system.