The invention discloses a method and device for testing in-band carrier leakage repression of a repeater. The method comprises the following steps of: sending a signal link opening command to the repeater so as to open one signal transmission link of the repeater; sending a signal output command to a signal generator, so that the signal generator generates a carrier signal Si input into the ith channel in a working frequency band of the repeater; adjusting the working frequency band of an adjustable bandwidth filter from fa to fi, and measuring a plurality of harmonic component points generated by the Si to the repeater between fa and fi through a spectrometer; adjusting the working frequency band of the adjustable bandwidth filter from fi to fb, and measuring a plurality of harmonic component points generated by the Si to the repeater between fi and fb through the spectrometer; and, according to all the harmonic component points, obtaining an in-band carrier leakage repression ratio corresponding to the ith channel and an in-band carrier leakage repression ratio of the repeater. By means of the method and the device disclosed by the invention, the precision of the obtained in-band carrier leakage repression ratio can be effectively improved.