The invention relates to the field of thermal control and automation, and discloses a rapid load reduction system and method for sharing water supply pumps between different unit-system units. The rapid load reduction system comprises a public water supply pipeline through which water supply pump pipelines of any two unit-system units are communicated, a regulation device arranged on the public water supply pipeline, and a control device. The regulation device is used for regulating the water supplementation amount of water supplementation conducted by the unit-system unit where water supply pump stripping does not happen on the unit-system unit where water supply pump stripping happens through the public water supply pipeline. The control device is used for judging whether the maximum water supplementation capacity of the unit-system unit where water supply pump stripping does not happen meets the water supplementation requirement for the unit-system unit where water pump stripping happens or not, controlling the regulation device to regulate the water supplementation amount if the maximum water supplementation capacity of the unit-system unit where water supply pump stripping does not happen meets the water supplementation requirement for the unit-system unit where water pump stripping happens, and controlling the unit-system unit where water supply pump stripping does not happen to conduct rapid load reduction and then controlling the regulation device to regulate the water supplementation amount if the maximum water supplementation capacity of the unit-system unit where water supply pump stripping does not happen does not meet the water supplementation requirement for the unit-system unit where water pump stripping happens. The rapid load reduction system and method solve the problem that when water feed pump stripping happens, unit outage happens because the output of a water supply pump of a single unit is not enough.