According to the phenomenon that the objects will generate sound signal under the irradiation of periodic light

a detection method of methane gas based on photoacoustic spectroscopy is proposed.According to Beer-Lambert law

when the modulated parallel beams is passing different volume fraction of methane gas

the light intensity will become attenuation in different degrees.If the decayed light go into a photoacoustic cavity

photoacoustic signal will be generated in the cavity.By measuring the amplitude of photoacoustic signal

the purpose of detecting the methane gas is achieved.Compared with usual spectral method

this method add a process that converting the heat energy into sound signal

which has high accuracy and reliability.It provide a theoretical basis for studying on high sensitive methane gas sensor.