In order to suppress the four wave mixing (FWM) effect, two improved schemes aiming at traditional wavelength division multiplexing (WDM) systems with equal frequency intervals are proposed according to the formation mechanism and main influence factors of FWM effect. One scheme is to design a channel spacing which is broad in the middle and narrows toward each end. Another scheme is to design the channel spacing with unequal intervals. A seven-channel WDM system is established and simulated with OptiSystem. The two schemes can suppress the FWM effect and the second one is better than the first one.