The invention discloses an operation mechanism of a small-sized circuit breaker. The operation mechanism of the small-sized circuit breaker comprises a handle, a transmission connection rod, a static contact, a dynamic contact, a tension spring, and a release lever. One end of the transmission connection rod is connected with a handle in a hinged manner, and the other end is cooperated with the dynamic contact. One end of the tension spring is fixedly disposed on the housing, and the other end is connected with the dynamic contact. The dynamic contact is driven by the tension spring and the transmission connection rod together, and contact pressure and over travel elastic force required by guaranteeing of electric contact reliability are provided for the closing of the dynamic contact and the static contact, and in addition, the tension is used to provide energy storage elastic force used for mechanism resetting required by the driving of the breaking of the dynamic contact and the static contact. The release lever is disposed on the dynamic contact, and is used to control the locking and unlocking cooperation between the transmission connection rod and the dynamic contact. The release lever is used to separate the transmission connection rod and the dynamic contact during occurrence of a fault, and then the operation mechanism is released automatically. The operation mechanism has advantages of effective structure simplification, production cost reduction, production efficiency improvement, and mechanism performance optimization.