At present, the existing dynamic model can not describe the motion characteristics of large-load glider accurately, and the conventional controllers are not ideal for the glider system with large time-delay and strong coupling. Aiming at these problems, the quality change of the internal and external oil sac is taken into account in the buoyancy driving mechanism and the centroid position vector change caused by the flow of hydraulic oil in the internal and external oil sac, further establishes the vector model with two particles and variable mass and variable position for the large-load underwater glider, which provides the theoretical guidance for the design and control of the glider. Based on the established model, the PID control method and the Active disturbance rejection control (ADRC) method are designed and the contrast experiments are done on both the pitch angle and velocity loop for glider by considering the influence of coupling disturbance and combining with the glider system parameters and actual working characteristics. The results show that the ADRC controller has higher control accuracy, faster response speed and lower overshoot than the PID controller, which make the glider have higher flexibility and longer endurance. Moreover, the ADRC controller is more suitable for the strong coupling large-load glider systems in complex marine environments due to the stronger ability of rejecting the internal and external disturbances.