The dominating effect of Wavelength Division multiplexed system is Four Wave Mixing (FWM).Channel crosstalk and performance degradation of the system can be induced in the multi channel systems by FWM. In this paper, we have simulated the effect of chromatic dispersion on FWM using equal channel spacing in terms input/output spectrum, eye diagram and bit error rate. Results show that the effect of FWM reduces with the increasing dispersion coefficient. And the suppression of FWM is achieved by placing the Optical Phase Conjugator (OPC) in the midway of the fiber optic link. It strongly suppresses the FWM signal by introducing the destructive interference between the first and second halves of the fiber optic link. Reconstruction of original signal can be achieved by placing another OPC at the end of the second fiber span. DWDM system with OPC can effectively suppress the Four Wave Mixing signal power.