The DC microgrid plays an important role in the effective utilization of distributed generation. To solve the problem that the real-time disturbance in a DC microgrid affects the control of the bidirectional DC-DC converter and worsens power quality, an expert system-changeable gain active disturbance rejection voltage stabilization control is proposed. First, the expert system is designed using state observer theory, and is organical combined with the ESO. A dynamic adjustment factor is introduced to realize the online optimization of the observer gain. Second, expert rules and changeable gain active disturbance rejection control strategies are formulated based on the observation absolute observation error and control strength demand of the system in the process of anti-interference, and the value range of the dynamic adjustment factor is given. In addition, the effects of observation tracking performance, disturbance rejection frequency domain characteristics, noise suppression and time varying gain on system immunily are analyzed theoretically. The analysis shows that the proposed control strategy can effectively improve the performance of the system. Finally, the simulation and physical experiment results show that the performance of ES-CGADRC is better than that of traditional double closed-loop PI and LADRC control in a variety of conditions.