To mitigate the impact of overlapping spectra on the accuracy of spectral information extraction， a multi-gas spectral detection method is proposed in this study， based on Sub-Doppler Noise-Immune Cavity-Enhanced Optical Heterodyne Molecular Spectroscopy （NICE-OHMS）. This method leverages high laser power excitation saturation absorption established within a high-finesse optical cavity， resulting in a significant enhancement in spectral resolution and a reduction in spectral interference caused by impurity gases. Furthermore， the incorporation of wavelength modulation techniques effectively eliminates the influence of residual Doppler background on the sub-Doppler signal. A wavelength-modulated sub-Doppler NICE-OHMS model has been developed， with experimental investigations conducted using the transition lines of C₂H₂ and NH₃ at 1 531 nm. The results demonstrate that， under conditions of a modulation frequency of 150 Hz and a modulation amplitude of 2.68 MHz， a sub-Doppler absorption signal of C₂H₂ exhibiting a saturation degree of 12.10 can be successfully excited within the optical cavity. Additionally， the sub-Doppler absorption of C₂H₂ is unaffected by the adjacent NH₃ spectra and the Doppler background. The sensitivity of the detection system is determined to be 1.163×10^-12 cm^-1 via Allan variance analysis. These findings confirm that this technique effectively eliminates spectral interference from impurity gases while maintaining high sensitivity and selectivity within the spectral system.