Abstract: Basing on the Gauss-Markov model and according to the basic functional model this paper distinguishes the different phase ambiguity in DEM generation and deformation extraction by establishing the phase unwrapping functions. Thereafter a refined D-InSAR functional model is proposed . According to the refined D-InsAR functional model some basic D-InSAR models have been derived, such as two-pass, three-pass and four-pass method. Some concise error analyses have also been give during the derivation.