The present invention provides an economizer, including a housing having a first section and a second section; and a condenser outlet, an evaporator inlet, and a compressor intermediate-stage inlet that are disposed on the second section of the housing; wherein the first section has a contour matching a housing of a commonly used condenser, such that the first section can fit the housing of the condenser. The economizer of the present invention can better match an outer contour of a conventional condenser, so that the both can fit each other in arrangement as much as possible when applied to an overall layout of a refrigeration system, thereby significantly reducing a transverse space occupied by the refrigeration system.