A heat exchanger that uses water liquid and vapor phases transformation to enhance heat exchange performance mainly includes a primary heat exchanger, a water vaporization device and an auxiliary heat exchanger. The auxiliary heat exchanger has an upper heat exchange tube on an upper end and a lower heat exchange tube on a lower end thereof. The upper and lower heat exchange tubes are connected by a plurality of vertical heat tubes. Refrigerant and water serve as heat exchange media to pre-cool (pre-heat) air intake. The auxiliary heat exchanger and water vaporization device can generate liquid and vapor phases transformation to increase water content in the air to enhance heat exchange effect of the air, thereby to enhance heat exchange performance of the heat exchanger, and save energy and reduce thermal pollution.