The invention relates to a working harmonic displacement judging method of a space-borne synthetic aperture radar. The judging method comprises the following steps: calculating the leading-edge and trailing-edge echo time of a transmitting signal and a sub stellar point interference fringe through parameters input and further calculating the slant range between a corresponding radar and an interference area according to results obtained and an visual angle of the interference area relative to the corresponding radar; and determining the congregation of pulse recurrence frequency and further judging the working harmonic displacement of a radar antenna and verifying judging results. The invention can complete the tasks by using a receiver without the arrangement mode of a plurality of traditional receivers, thereby saving labors and materials and providing essential information for identifying the reconnaissance intention of a synthetic aperture radar satellite of adverse party and organizing the effective deceiving interference of the synthetic aperture radar satellite of own party.