The invention relates to a range-adjustable operating mechanism assembly and a circuit breaker. The range-adjustable operating mechanism assembly comprises an operating mechanism, wherein the operating mechanism is provided with an output end which can move in a reciprocating way, the operating mechanism assembly also comprises a lever, the lever is in transmission matching with the output end, comprises a power arm segment and also comprises a resistance arm segment, the power arm segment is connected with the output end, the resistance arm segment is used for being in transmission matching with a movable end of an arc extinguishing chamber, and the length of the power arm segment and/or the resistance arm segment is adjustable. The range adjustment is achieved by changing the size ratiobetween a power arm and a resistance arm of the lever, the purpose of the range adjustability is achieved, thus, the defect that a traditional large-range circuit breaker cannot be matched and adaptedcan be changed, more large-range circuit breakers can be expected to be adapted, the phase selection accuracy of a large-range phase-selection circuit breaker is substantially improved, more circuitbreakers are adapted, a large-scale effect is brought, the cost is further reduced, and the corresponding economic benefit is brought.