Focusing on parametric uncertainties and environmental disturbances, an active disturbance rejection attitude control method is proposed for a class of morphing aircraft, based on a fully actuated system model. Firstly, the strict-feedback system model of the morphing aircraft with time-varying coefficient matrices is transformed into a second-order fully-actuated system model. Then, Active Disturbance Rejection Control (ADRC) scheme is employed to address the attitude control problem of morphing aircraft. The internal parameter perturbations, matched and unmatched disturbances, and difficult-to-measure differential terms generated by model transformation are treated as total disturbance, which is estimated using an extended state observer and dynamically compensated through feedback. A concise linear state error feedback law is designed to control the disturbance-compensated system. The proposed active disturbance rejection control method, uniquely based on a fully-actuated system model, offers a simplified design process and a concise control law with minimal tuning parameters. It effectively handles parameter uncertainties and external disturbances, meeting the high-precision and robust attitude control requirements of morphing aircraft. Numerical simulation results demonstrate that the proposed control method ensures stable and precise control under external disturbances and large-scale perturbations of aerodynamic parameters and moment of inertia up to ±50%, exhibiting strong robustness. Compared with the conventional backstep-ping-based active disturbance rejection control structure, the proposed method reduces the computational time of control inputs by 12%.