Abstract: The aim of this paper is to identify the relationship between the contact bouncing time and the performance of vacuum circuit breakers.The factors that affect bouncing time are described and explained.It is easy to measure the contact bouncing time of vacuum circuit breakers（VCB） during no-load operations.Considering the relationship between the contact bouncing time and the performance of vacuum circuit breakers,some typical duties such as making/breaking operations under short-circuit conditions,load current switching,single capacitor bank and back-to-back capacitor bank charging current switching are examined in some detail.The results prove that the contact bouncing measured during no-load operations is unrelated with the actual bouncing during current breaking,either under normal or abnormal conditions.The article also analyzes the origin of the currently existing requirement for the maximum allowable bouncing time.The final conclusion is that the contact bouncing time has no impact on the performances of vacuum circuit breakers.Therefore it is not useful to set up arbitrary limitations on the value of this parameter in standards or customer technical specifications for circuit breakers.