H2S and moisture content are important indicators to evaluate the potential faults and insulation performance of H2S electrical appliances. Currently, there is no report on the simultaneous detection of H2S gas and moisture content. In order to realize the accurate detection of H2S gas and H2O at the same time, Lorentz simulation analysis was performed on the absorption spectra of H2S gas and H2O molecules. The absorption was strongest near 2684nm, and there was no cross interference of SF6 other decomposition products. H2S and moisture content at different concentrations were measured by TDLAS technology in a customized CW-DFB laser with a central wavelength of 2.68μm combined with a small-volume Herriott long-range cell with multiple reflections. In order to verify the detection ability of selected spectral lines to H2S gas and H2O molecules at low concentration, trace H2S and H2O vapor with SF6 as background were detected by direct absorption technology and wavelength modulation technology respectively. In the second harmonic absorption, the minimum detection lower limit of H2S and H2O is 9.01×10-6 and 4.54×10-6, respectively. The maximum harmonic signal amplitude has a good linear correlation with concentration, and the linear fitting degree R2 is 0.978 and 0.997, respectively. SF6 gas displacement experiments with different flow rates showed that the equilibrium time of H2S and moisture content at 708mL/min was 90s and 100s, respectively. The response time of H2S and H2O at the same concentration and injection velocity is 30s and 45s, respectively. Wavelength modulation technology can provide a reliable experimental basis for the simultaneous detection of trace H2S and H2O in high voltage combination electrical appliances.