Phase unwrapping is a key step of three-dimensional display in digital holographic microscopy(DHM). On the basis of the framework of Lp-norm,the unified mathematic model of two-dimensional phase unwrapping is studied. A wrapped phase map of DHM is analyzed with several phase unwrapping methods. The results show that the L0-norm algorithm performed best in efficiency,but got wrong result because of too much noise,the L1-norm algorithm could achieve an better resolving,but the most long time consuming,the Lp-norm algorithm used much iterative,but also resulted with aberrations and the efficiency was rather low,the least-squares algorithm and the weighted least-squares algorithm could obtain better optimal resolving and better efficiency. The two algorithms are acceptable in DHM.