A CO sensor system based on quartz-enhanced photoacoustic spectroscopy technology was established to study the effect of sulfur hexafluoride (SF6) and water vapor (H2O) on the relaxation rate of carbon monoxide (CO) gas molecules. A 1.57 μm near-infrared distributed feedback diode laser was used as the light source to compare the photoacoustic signal amplitudes of CO under different concentrations of SF6 and H2O. First, a CO sensor system was used to detect photoacoustic signals from CO in a gas mixture of CO and N2. Then, different concentrations of SF6 gas were added to the CO and N2 gas mixture and the photoacoustic signal amplitudes of CO were detected. Finally, H2O was added to the gas mixture of CO and N2 before detecting the photoacoustic signal amplitudes of CO. The experimental results show that with increasing concentration of SF6 in the gas mixture of CO and SF6, the photoacoustic signal of CO remains constant; however, the addition of 2.5% H2O to the mixture results in a five-fold increase of the photoacoustic signal of CO. Therefore, H2O has an obvious effect on the relaxation rate of CO gas, while SF6 has none.