A circuit breaker comprising a fast closing mechanism, wherein the fast closing mechanism is configured to be mounted on a side plate of the circuit breaker, the fast closing mechanism comprising: a rotation shaft and an ejector pin configured to be rotatably assembled to the side plate by the rotation shaft, wherein the ejector pin comprises a first portion and a second portion, the first portion being configured to be located at an inner side of the side plate and the second portion being configured to be located at an outer side of the side plate, the first portion being connected to a handle via a rod, and the second portion being configured to be located above a press plate, wherein the first portion comprises a longitudinally extended rod part and a laterally extended top part including a sliding groove, the rotation shaft is mounted on the longitudinally extended rod part, and the longitudinally extended rod part is configured to stride over the side plate and connects to the second portion of the ejector pin, wherein the rod has a projection configured to slide within the sliding groove and the ejector pin is configured to rotate when the projection touches an end of the sliding groove, wherein the press plate is configured to press against a moving contact of the circuit breaker at an initial stage of a closing process, so that the moving contact will not be actuated via the ejector pin during the initial stage of the closing process in which the handle is actuated, and wherein the mechanical energy generated during the closing process is stored in an energy storage spring such that at a later stage of the closing process, the ejector pin releases the press plate, the press plate and the moving contact obtaining an initial speed by the spring force of the energy storage spring so as to accomplish closing. a rotation shaft and an ejector pin configured to be rotatably assembled to the side plate by the rotation shaft, wherein the ejector pin comprises a first portion and a second portion, the first portion being configured to be located at an inner side of the side plate and the second portion being configured to be located at an outer side of the side plate, the first portion being connected to a handle via a rod, and the second portion being configured to be located above a press plate, wherein the first portion comprises a longitudinally extended rod part and a laterally extended top part including a sliding groove, the rotation shaft is mounted on the longitudinally extended rod part, and the longitudinally extended rod part is configured to stride over the side plate and connects to the second portion of the ejector pin, wherein the rod has a projection configured to slide within the sliding groove and the ejector pin is configured to rotate when the projection touches an end of the sliding groove, wherein the press plate is configured to press against a moving contact of the circuit breaker at an initial stage of a closing process, so that the moving contact will not be actuated via the ejector pin during the initial stage of the closing process in which the handle is actuated, and wherein the mechanical energy generated during the closing process is stored in an energy storage spring such that at a later stage of the closing process, the ejector pin releases the press plate, the press plate and the moving contact obtaining an initial speed by the spring force of the energy storage spring so as to accomplish closing.