The impact of XPM effect on the pulse transmission in the NOLM switch with high working speed in the single wavelength channel and WDM 4-wavelength channel is analyzed by the split-step Fourier method based on the coupled nonlinear Schrodinger equation. The simulation results show that XPM induces the crosstalk and aberration of signals and deteriorates the switching performance of NOLM. Furthermore,the impact of XPM crosstalk of wavelengths of the pulse is far more than that of XPM effect of counterpropagating pulses in the fiber loop in the WDM system. The shorter the wavelength is,the lower the output power of NOLM is. The pulse pedestal and walk-off effect induced by XPM in the middle wavelength channels are more than those in the edge wavelength channels.