With the development of information infrastructure, the bit rate and the transmission distance of optical fiber communication are continually increasing. In high speed optic communication systems of 40Gbit/s and above, the effect of PMD to system has drawn more attention nowadays. PMD is an important limiting factor in transmission capacity. In this paper, a summary of the related concepts of PMD and its statistics nature is given firstly, which are the fundamentals for further discussion, and an optical fiber PMD model is given too. Then based on the model current popular PMD compensation methods are summed up. Analysis of the PMD compensation system within the general framework is also given. The degree of polarization as feedback signal in the compensation system is studied. Firstly the theoretical curves for DOP versus DGD are given, and they are simulated. Then the first and second order PMD compensation model are built, and the feedback control algorithm is written, and the comparison with the compensation system based on the electric power feedback is also given. Finally, the theory and simulation of DOP ellipsoid is given.