As submarine cables applied in usually complicated environment are subject to water pressure

impact and subterranean flow

the resulted stochastic Polarization Mode Dispersion（PMD） has become a limiting factor for the system extreme transmission.In this paper

the effects of such external factors as lateral stress and bending on PMD are theoretically analyzed and simulation of the 4×2.5 Gbit/s communication system is performed in accordance with the actual work conditions of the cable

taking 3 dB as the power redundancy.Simulation results show that when the communication system works normally

the PMD coefficient does not exceed 1.8 ps/km.In order to avoid PMD compensation

the lateral stress is not to be greater than 8.9 N/m when the bending radius is 0.3 m.