The invention provides a GB-SAR deformation monitoring method based on triple stepping. According to radar system design, GB-SAR based on triple stepping is utilized for deformation measurement; for first stepping, stepped frequency continuous wave (SFCW) signals are employed to synthesize large signal bandwidth, isolation is improved through transceiver antenna separation; for second stepping, a radar device is mounted on a linear guide rail and does stepping motion in a stop-go-stop mode, orientation resolution is improved through relatively large aperture synthesis, signals are emitted and received by the radar device in stop periods, so a phase error caused by signal transceiving in motion periods is avoided; for third stepping, radar device antennas do stepping motion sequentially along the orientation, a relatively wide monitoring area is covered, and data at different antenna positions are spliced and are used for imaging processing. Imaging processing on acquired data is carried out based on echo signal characteristics of the GB-SAR system, compensation for an instantaneous slant range difference between pulses is not necessary, computational complexity is relatively low, and timeliness requirement of the GB-SAR system can be satisfied.