Aiming at the fracture of the drive pin during the mechanical life test of a certain type of circuit breaker, the characteristics of the fracture site of the pin are studied, the simulation model is established, and the force of the pin shaft is simulated by finite element method. Tensile test sample was designed according to the shape of fracture pin, and tensile test was carried out to detect the mechanical properties of the pin material. Based on the above analysis, the causes of pin fracture are obtained, and the improvement measures are put forward to effectively improve the mechanical stability of the circuit breaker.