The performance of an optical wavelength division multiplexed communication system is analyzed taking the four wave mixing (FWM) effect into account. Also it is found that the efficiency of FWM generation can be greatly reduced by making the spacing between channels unequal. Taking into account the various channel spacing schemes and various distribution of different dispersion type optical fibers a comparative picture has been drawn to suggest the most efficient system with maximum FWM reduction. During the evaluation the FWM process in EDFA is also taken into consideration.