The operating mechanism and its electronic control circuit are the main components that affect the reliability of high-voltage breaker. The development of intelligent and digital switches demands higher requirements for the reliability of the switch mechanism. It is of great application value to research on modular circuit breaker mechanism for improving the reliability of switch operation. This paper studies the modularization transformation method of the circuit breaker mechanism, and proposes a modular design scheme of the secondary system of the circuit breaker mechanism, including the primary part of the mechanism and the modularization of the secondary circuit. The modularization of the primary part of the mechanism realizes the overall modular improvement of the mechanism box and the modular design of the components, and the modularization of the secondary circuit integrates the discrete secondary components into five functional modules. A quick replacement method of circuit breaker mechanism is also studied, the consistency of mechanism output is kept by technical means to realize the on-line replacement of different mechanisms. The accelerated aging test method is designed and the modified circuit breaker mechanism is tested with the method. The results show that the reliability of the modified mechanism meets the requirements.