Three-phase un-synchronization time is an important parameter to reflect the mechanical characteristics of circuit breakers. For the shortage that the traditional detection method can only be carried out under power-off conditions， A new ultrahigh frequency （UHF） method for detecting non-synchronous characteristics of circuit breakers is proposed， the detection principle of which is introduced， the experimental model is established in the laboratory， and the feasibility is studied and measurement is conducted on the spot. The results show that the UHF method can realize the non-contact detection for un-synchronization time of circuit breakers. The research results have the value of further popularization and application.