Abstract: A new phase unwrapping algorithm with difference filter for multi-band InSAR was proposed by taking zero intermediate frequency vector filtering of interferogram for reference. It differences the interferogram with shorter wavelength to the one with longer wavelength to reduce the frequencies of fringes, as can improve the effects of filtering and phase unwrapping. It unwraps the phases with shorter wavelength based on the unwrapped phases with longer wavelength. All the phases in interferograms with different bands are used in phase unwrapping, so the reliability and the precision of phase unwrapping are improved. The simulated multi-band interferograms from DEM were applied in phase unwrapping experiments. The unwrapped phases were satisfying, as validated the proposed phase unwrapping algorithm.