In ultra-high speed coherent fiber optical communication systems,the improvement of single-carrier signal rate is usually considered as the foundation for rate improvement of wavelength division multiplexing (WDM) and even the entire communication system.During the process of single-carrier rate improvement,polarization mode dispersion (PMD) is considered to be one of the most important factors restricting the rate improvement of fiber optical communication systems.Conducting corresponding PMD simulation calculations is expected to provide PMD solutions for breakthrough rates on the one hand; On the other hand,it can lay a good foundation for subsequent Tb/s rate experiments and commercial use.This article quantitatively analyzes the impact of first-order,second-order and higher-order,full-order PMD on coherent fiber optical communication systems at the single-carrier rate of Tb/s level from the perspective of error vector magnitude (EVM) and symbol error rate (SER).Secondly,the constant modulus algorithm (CMA) is analyzed for first-order,second-order and higher-order,full-order PMD compensations.Finally,the optimal tap numbers of the CMA algorithm are calculated for three cases of PMD.The results show that the optical signal-to-noise ratio (OSNR) tolerance limit of the system can be improved by 6.7 dB and 6 dB,respectively,when only the first-order,second-order and higher-order PMD is included.When the single-carrier rate reaches 1.2 Tb/s,the compensation effect of the CMA algorithm for second-order and higher-order PMD is better than first-order PMD,and the optimal tap numbers are different in three cases.