The invention discloses an interferometer system based secondary surveillance radar response signal direction-finding method, which relates to the technical field of radio monitoring. The method comprises the following steps that: a 4-array-element direction-finding antenna array with a receiving sidelobe suppression antenna unit receives secondary radar response signals, and four receiving channels respectively carry out digital measuring on frequency, amplitude and phase parameters; then, an operation of controlling the receiving sidelobe suppression of an instantaneous direction-finding range and an operation of exhaustion based long-short baseline resolving phase ambiguity are performed; and finally, the orientation resolving is completed through phase orientation mapping. A secondary radar response signal direction-finding system using the method disclosed by the invention has the advantages of high direction-finding precision, rapid direction-finding speed, large instantaneous direction-finding range, low power consumption, low cost, capability of carrying out passive direction-finding, and the like, and has a good application prospect and economic benefits in promoting the air surveillance range in the field of air management and monitoring.