The invention relates to the technical field of electrotechnics and electronics, discloses a diagnostic method for the mechanical fault of a circuit breaker and a device for the mechanical fault of the circuit breaker, and aims at solving the technical problem that the diagnosis on the mechanical fault of the circuit breaker is not accurate enough in the prior art. The method comprises the following steps of detecting and obtaining the current waveform of a circuit where an electromagnet coil of the circuit breaker is located in the case of operating the circuit breaker; extracting first characteristic parameters of the circuit breaker from the current waveform, wherein the first characteristic parameters comprise five characteristic moments and four current amplitude parameters; based on a corresponding relationship between the characteristic parameters and mechanical states, determining a first mechanical state, which corresponds to the first characteristic parameters, of the circuit breaker, wherein the first mechanical state represents a mechanical fault state of the circuit breaker. By applying the method and the device, the technical effect that the diagnosis on the mechanical fault of the circuit breaker is more accurate and more convenient is realized.