Abstract: Phase unwrapping is one of the key techniques of multi-baseline InSAR.In order to provide algorithms for phase unwrapping of multi-baseline InSAR,zero intermediate frequency vector filtering algorithm was used for reference.A new phase unwrapping algorithm based on difference filtering was proposed by inducing difference filtering to phase unwrapping.In this method,phase unwrapping of interferogram with longer baseline was guided by the unwrapped interferogram with shorter baseline,the un-fuzzy phase interval of phase unwrapping was extended,and the difficulty of phase unwrapping for sub-sampling area in interferogram with longer baseline was solved.The multi-baseline phase unwrapping experiments were done with simulated interferograms from DEMs of SRTM and SIR-C/X-SAR.The satisfying phase unwrapping results have been gotten.