A sliding-mode decoupling control strategy based on an extended state observer （ESO） is proposed for the problem that the output branch of a single-inductor dual-output Buck converter suffers from severe crossover effects and slow transient response when load disturbances occur. Firstly， considering the load disturbance problem， the system model is transformed into the output voltage deviation model.And the main circuit ESO is designed to estimate the load disturbance and compensate the disturbance estimation information to the improved reaching-law backstepping sliding-mode controller of the main circuit switching tubes. Next， considering the branch circuit coupling problem， a branch circuit is fitted as an independent system based on the self-anti-disturbance paradigm， where the branch circuit coupling term and the external disturbance are regarded as the total disturbance.And the branch circuit ESO is designed to estimate it， and a sliding mode and active disturbance rejection controller is constructed in the branch circuit switching tube based on the disturbance estimation information and the sliding-mode control algorithm. Finally， the closed-loop stability of the main and branch circuit controllers is demonstrated using the Lyapunov theory. The simulation results show that the control strategy significantly reduces the cross-influence between the branches and improves the transient response speed of the system.