Abstract: The energy storage mechanism of a 35kV spring circuit breaker is introduced. In response to a fault caused by insufficient pre-compression amount of the closing spring, which resulted in the inability to open the circuit breaker normally, on-site inspection and testing were conducted after isolating the abnormal switch. Subsequently, the abnormal components of the circuit breaker mechanism were disposed of and tested. A comprehensive analysis of the cause of the abnormality was performed, providing a reference for the diagnosis and handling of similar faults in circuit breakers of the same model.