The signal degree of polarization（DOP） of RZ are calculated with the consideration of polarization mode dispersion（PMD） and nonlinear effect in the WDM system of using the coupled nonlinear Schr?dinger equation

and we get the all channel’s eye diagrams of RZ and NRZ

finally we get the relationship figure of the signal DOP and wavelengths. By contrast the eye diagrams with the DOP- graph

we can see that the effects of PMD on the various channels are very different

and comparing the results of the two methods

we verify that the signal DOP can be used in WDM system to detect channels’ performance in compensating for the worst PMD in real time .