The estimation formula of transmission bandwidth of WDM system using optical phase conjugator (OPC) at the midpoint of standard fiber link for dispersion compensation is derived and verified by numerical simulation. The OPC is asymmetrically accessed in the fiber link to improve transmission bandwidth and the estimation formula of transmission bandwidth affected by OPC accessing position is derived. The results of both estimation and numerical simulation show that the transmission bandwidth of WDM system with OPC at the optimum position is increased nearly by one time as compared to that of WDM system with OPC at the midway.