Abstract: Phase unwrapping is usually defined as the reconstruction of the real value of the phase from the principal value. In addition to the application of radar interferometry, phase unwrapping is also applied significantly in the synthetic aperture sonar, adaptive optics, nuclear magnetic resonance, seismic processing and so on. Multi-baseline can improve the performance of phase unwrapping. This paper, used the multi-baseline interferometric synthetic aperture radar (InSAR) system as the application background, proposes a rapid method for the multi-baseline InSAR interferometric phase unwrapping in frequency domain. The basic idea is to make the least square of the weighted difference between the frequency domain function of the phase gradient estimated value and of the baseline phase gradient. Both simulated and real data processing results show that the frequency domain method has similar effect as the time domain method, while its efficiency is greatly improved by avoiding the mirroring operations.