Considering the internal and external disturbances in actual engineering structure, a composite active vibration control method is proposed for an all-clamped piezoelectric panel. First, the theoretical modal analysis and laser vibrometer are employed to obtain the natural frequency and mode shape of the panel, for reasonable arrangement of actuator and accelerometer. Second, a nonlinear extended state observer is introduced to estimate the total disturbances, i.e., modeling uncertainties, high-order harmonics, coupling and external excitations. Third, the estimated value is used to compensate and attenuate the influence of the total disturbances in real time. In addition, the feedback controller based on the proportional differential and acceleration feedback method is designed to enhance the vibration suppression performance of the whole system. Finally, a semi-physical platform is built in MATLAB/Simulink real-time environment with the NI-PCIe6343 acquisition card to verify the effectiveness and superiority of the proposed method.