In order to finish the phase unwrapping of multi-baseline InSAR (Interferometric Synthetic Aperture Radar) to combine data with longer and shorter baselines and derive accurate DEMs (Digital Elevation Models), a phase unwrapping model with linear congruent equations is designed and its solution with the Chinese Remainder Theorem (CRT) is presented in detail. In this algorithm, the un-fuzzy phase interval of phase unwrapping is enlarged by forming the congruent equations. The SRTM (Shuttle Radar Topography Mission) DEM was used to simulate multi-baseline interferograms to do phase unwrapping experiments. There are sub-sampling areas in simulated interferograms, as can lead to wrong phase unwrapping results in single baseline phase unwrapping algorithm. However, the right phase unwrapping results were got with the CRT phase unwrapping algorithm, as validated it.