Environmental influence is the important factor in a photoacoustic spectroscopy gas detection (PASGD) system when it is applied in the industrial field. The experiments show that the sensitivity of condenser microphone is affected mostly by the humidity of the gas under test, leading to the PASGD’s result drift. The present paper puts forward a method to eliminate the influence of gas humidity. A speaker is fixed in the photoacoustic cell, whose amplitude is regarded as the sensitivity self-adaption characterization of sound sensor, used to correct the photoacoustic signal amplitude. Thus the problem of sensitivity changing in sound detection with condenser microphone is solved. Based on this method, a photoacoustic experimental setup, equipped with a diode laser, a resonant photoacoustic cell and a lock-in amplifier, was applied to compare the test for different humidity samples. The results show that this method is useful to eliminating the gas humidity influence and enhancing environmental adaptability of PASGD system.