In this paper, the optimal values of optical phase conjugator (OPC) position and dispersion coefficients of fiber sections depending on the extinction ratio of WDM channel signals are numerically induced in WDM system with OPC used to compensate the distorted signals due to nonlinearities and chromatic dispersion. The considered WDM system consist of 16 channels with 40 Gbps data rate and each channel is assumed to be NRZ format with the extinction ration of 5 dB, 10 dB, or 20 dB. It is confirmed that the only one parameter among two considered parameters is used to effectively compensate overall WDM channels, and each optimal value of these parameters independent on the extinction ratio. That is, overall WDM channels are excellently transmitted within 2 dB power penalty whether by positioning OPC into 496 km or by setting dispersion coefficient difference between two fiber sections to 0.055 ps/nm/km, these optimal values are not dependence on the extinction ratio.