Abstract: This paper proposes a fast switching device renovation plan based on improved fuzzy self disturbance rejection control to address the problems of large switching current, severe bus voltage drop, and low switching success rate in the traditional fast switching device of the 660 MW thermal power unit high-voltage plant power system, and conducts reliability analysis. This article adopts a tracking differentiator to safely transition the process, extracts high-quality reference inputs and differential signals, and uses an extended state observer to estimate and dynamically compensate for system disturbances in real time. At the same time, a fuzzy logic reasoning module is introduced to achieve self-tuning of controller parameters, ensuring the optimality of parameters under various operating conditions. The experimental results show that the fast switching device designed in this paper can limit the impulse current during the switching process to within 1.2 times the rated value, laying an important foundation for the safe and stable operation of thermal power units.