An adaptive optimum path method and least mean square (LMS) phase unwrapping as a typical path-independent method are discussed. In the latter case Poisson equation and its discrete formulation are derived. The multigrid algorithm for solving this equation is given in detail. Especially a weighted multigrid algorithm aimed at cases with boundary and blockage is presented. Then a modified multigrid algorithm which combines the advantages of two classes of phase unwrapping algorithms is developed. It takes the results of the adaptive optimum path method as initial guess of the iteration of multigrid and a high accuracy is reached within a considerably faster convergence speed. In the simulation experiment an interferogram of a flow field containing opaque objects and the related results are given. The method is applied to a real interferogram and is proved that it is effective and practical for reconstructing wave-front containing opaque object.