Abstract: Solid-state transformer (SST) is the core equipment of energy router to realize energy conversion. As distributed generation units are often in multivariable, strong coupling and violent unknown disturbance, the stable operation of the system is severely challenged. In order to solve this problem, a sliding mode active disturbance rejection controller based on improved linear extended state observer (LESO) is designed and applied to the voltage outer loop of the rectifier stage of solid-state transformer. New errors were introduced to the traditional LESO to adjust various state variables, and the observation accuracy of LESO was improved. The state variables observed by the improved LESO were used in sliding mode controller (SMC) for feedforward compensation adjustment to reduce the random fluctuation of DC bus voltage caused by disturbance. The system was verified by the simulation platform. The results show that the sliding mode ADRC based on the improved LESO can obviously improve the dynamic performance and grid-connected quality of the system.