In order to reduce the crosstalk in the channel, reduce the channel error rate, and improve the communication quality due to the non-linear effects such as Four-wave Mixing (FWM) in Wavelength Division Multiplexing (WDM) all-optical network, the mechanism of FWM in WDM all-optical network transmission system is analyzed, and a scheme combining the dispersion compensating grating with the wavelength assignment is presented. In 2-7 channel system, this scheme is numerically experimented with traditional scheme, wavelength assignment scheme, 100 GHz channel spacing scheme, and using dispersion compensated grating scheme. With the increase of the number of channels in the WDM all-optical network system, the effect of wavelength allocation scheme decreases gradually, while the effect of using the dispersion compensation grating to suppress the FWM effect increases gradually, and the dispersion value of the dispersion compensation grating also increases gradually. When the number of channels is small, using the wavelength assignment scheme, the average error rate of the channel is 6.5×10-217, and the average error rate of this scheme can reach 1.07×10-235. When the number of channels is large, using the dispersive compensated grating scheme, the average error rate of the channel is 1.36×10-51, and the average error rate of this scheme can reach 3.34×10-63. The results are of great importance to the minimization of FWM in WDM optical networks.