The invention relates to a circuit breaker, a spring operating mechanism thereof and a chain energy storage device. The chain energy storage device comprises a power input shaft, an energy storage shaft, a first pulley rack and a second pulley rack. An input shaft sprocket is arranged on the input shaft. An energy storage shaft sprocket is arranged on the energy storage shaft. A first movable pulley is arranged on the first pulley rack. A second movable pulley is arranged on the second pulley rack. The input shaft sprocket, the energy storage shaft sprocket, the first movable pulley and the second movable pulley are wound by closed-loop chains. The chain energy storage device further comprises a closing buffer. The connection structure between the closing buffer and a device rack or the connection structure between the closing buffer and the first pulley rack is a shaft and long hole connection structure. The shaft and long hole connection structure comprises a first long hole with length extending in vertical direction and a sliding shaft in guide movement matching with the first long hole. The invention provides the chain energy storage device with a closing buffer function, the spring operating mechanism and the circuit breaker, wherein the spring operating mechanism and the circuit breaker use the chain energy storage device.