The accuracy of measurement is affected by the variation of water vapor concentration when a quartz enhanced photo-acoustic spectroscopy (QEPAS) is used for real-time trace-gas monitoring. A QEPAS based methane sensor is developed at 1.653 μm and the influence of water vapor on the performances of QEPAS methane sensor including second harmonic signal, resonance frequency, Q factor are investigated experimentally. Measurements are carried out under different absolute humidities which are obtained by bubbling method combined with hygrometer at atmosphere pressure. The results suggest that the water vapor could impact both on relaxation time of methane and the parameters of quarts tuning fork in practical application. The smallest detective mass concentration of the sensor is found to be about 0.57 mg/m3 at different atmosphere pressures with an absolute humidity of 2.34%.