The invention discloses a vacuum circuit breaker for an air-insulated ring main unit. The vacuum circuit breaker comprises a spring operation mechanism and a circuit switch protection mechanism. The circuit switch protection mechanism arranged in a housing consists of three-phase vacuum protection units, linkage mechanisms corresponding to all phases of vacuum protection units, and a transmission shaft; the linkage mechanisms are in transmission connection with the transmission shaft and the corresponding phases of vacuum protection units so as to realize opening or closing of the vacuum protection units and cutting of transmission control; and the transmission shaft is installed in the housing in a rotation manner and one end of the transmission shaft extends out of the housing and is connected with the spring operation mechanism. The vacuum circuit breaker has a simple structure and is designed skillfully. While the inter-phase insulation of the circuit breaker is ensured, the inter-phase distance is shortened to realize miniaturization and modularization of the circuit breaker and convenient installation and post maintenance of the circuit breaker. Moreover, the overall mechanical strength of the circuit breaker is improved; the service life is prolonged; and the great market value is realized.