To the methane gas with the concentration lower than 0.5%VOL,an optical methane gas sensor was designed based on near infrared tunable diode laser absorption spectroscopy.The methane gas absorption spectroscopy of 1 653.72 nm was scanned by tunable laser,and the gas concentration was measured by using the first harmonic PAPR.The proposed can effectively eliminate the influences caused by light intensity fluctuation of the laser and other kindred light power fluctuations,and the test results show that the precision of this kind of sensor can be 0.02%VOL.