The invention discloses a circuit breaker and an assembling structure of a three-phase linkage transmission mechanism thereof. The circuit breaker comprises a circuit breaker shell and a three-phase linkage transmission mechanism; the three-phase linkage transmission mechanism comprises a transmission shaft and a group of supporting plates fixed on the circuit breaker shell through bolts; an assembling hole used for assembling the transmission shaft and three connecting holes for respectively allowing the bolts to penetrate are arranged in the supporting plates; bolt holes corresponding to the connecting holes are arranged in the circuit breaker shell; the bolts are eccentric bolts; each eccentric bolt comprises a head part and a rod part eccentrically arranged on the head part; the internal diameter of the bolt hole is larger than the largest external diameter of the rod part; and the eccentric bolt further comprises a positioning column which is fixed on the rod part between the head part and the rod part and matched with the bolt hole when the rod part penetrates through the connecting hole. The circuit breaker with the structure provided by the invention can be used for solving the problem that the bolts cannot be connected due to deviation of the circuit breaker shell while the coaxiality of the assembling holes of the three supporting plates can be ensured, thus, the assembling of the supporting plates and the circuit breaker shell can be realized easily.