When the SIDO Buck converter is disturbed by the load, there is a serious cross-coupling between the branches. At the same time, the output signal is susceptible to uncertain factors such as high-frequency measurement noise. Aiming at the above problems, an improved sliding mode active disturbance rejection control strategy based on high-order filtering super-twisting extended state observer is proposed. Firstly, according to the mathematical model of SIDO Buck converter, the uncertain factors such as internal parameter influence and external disturbance are separated into lumped disturbance, and the auto -disturbance rejection model without considering physical parameters is established. Secondly, a high-order filtering super-twisting extended state observer is designed to achieve more accurate estimation and compensation of lumped disturbances, improve the ability to suppress noise and cross-effects, and prove its stability according to finite-time stability theory. Then, an improved super-twisting sliding mode feedback control law is designed to ensure that the sliding mode phase and the arrival phase can converge quickly, and the chattering is better suppressed. The stability of the feedback control law is analyzed by selecting the Lyapunov function. Finally, the superiority of the proposed control strategy is verified by simulation and experiment, which effectively reduces the cross influence, suppresses the noise and improves the transient performance of the system.