Increasing the active vibration isolation capability between the optical payload and the motion platform has always been a challenge for optoelectronic tracking systems. Therefore, a dual observer method is proposed to achieve wide-band disturbance rejection for an inertially stabilized platform. The dual observer method consists of two aspects. Firstly, a classical error observer has a strong low-frequency suppression ability through the design of a low-pass filter. Secondly, a saturated acceleration disturbance observer improves its disturbance suppression characteristics and completes the rejection of medium and high-frequency disturbances by adjusting the saturation threshold and filter bandwidth according to its stability conditions. The dual observer combines both advantages, and the interaction between the two observers is analyzed for better parameterization. Closed-loop verification of the proposal is carried out using the inertial stabilization device. The experimental results show that the dual observer can improve the closed-loop performance under both single-frequency and mixed-frequency disturbances.