The invention discloses an operating mechanism for a circuit breaker. The operating mechanism for the circuit breaker comprises a switching-on module unit and a switching-off module unit. The switching-on module unit is composed of a left side board, a right side board, an energy storage motor, an energy storage compression spring, a crank arm, an energy storage shaft, a cam, a chain wheel, a tripping shaft, a trigger, a microswitch, a switching-on electromagnet and an energy storage sign board. The switching-off module unit is composed of a left side board, a right side board, one or more tripping electromagnets, a switching-off half shaft, a pinch plate, a trigger and a switching on / off sign board. The operating mechanism for the circuit breaker has the advantages that the operating mechanism is practical and low in production cost, and the spring operating mechanism of the circuit breaker is combined into a modularized unit, is independent from the circuit breaker, and is integrally assembled and disassembled conveniently; a switching on module and a switching off module in the modularized operating mechanism can be independently assembled in advance and are each of one specification, and therefore the variety and the number of spare parts and stored parts are both greatly reduced, and the production efficiency of products is improved.