A new phase unwrapping algorithm based on reliability ordering was proposed.The key of the algorithm is to point out the dependability of data by choosing coherence maps.The way for phase unwrapping is guided by coherence maps.The fundamental rule of reliability ordering was elaborated,and the algorithm design and the flow diagram were discnssed.The phase data obtained by the Interferometer synthetic aperture radar(InSAR) had been unwrapped,and we obtained the relatively ideal results.The experiments indicate that the way of phase unwrapping is always from the high dependability pixels to the low dependability pixels.Therefore in the worst instance,the errors are limited in the smallest local region to a large degree.