Disclosed in the present application are an economizer and a refrigeration system comprising same. The economizer comprises: an outer shell that internally comprises a heat exchange cavity and a gas-liquid separation cavity; and a heat exchange tube bundle provided in the heat exchange cavity. The economizer is configured to enable refrigerants from a condenser to be subjected to heat exchange in the heat exchange cavity first, and then to be subjected to gas-liquid separation in the gas-liquid separation cavity after passing through a first-stage throttling device, such that gas refrigerants flow out of a gas outlet of the gas-liquid separation cavity, and liquid refrigerants flow out of a liquid outlet of the gas-liquid separation cavity. According to the economizer of the present application, the heat exchange cavity and the gas-liquid separation cavity are provided in the shell, the gas-liquid separation function of the economizer can be achieved, the heat exchange function of a subcooler can also be achieved, such that the structure of the two-stage compression refrigeration system with the function requirements of the subcooler can be more compact.