A methane gas sensor system based on tunable diode laser absorption spectroscopy is designed, mainly aiming at wide temperature range, full concentration, high precision of real-time testing instruments. The feature of high sensitivity is accomplished by choosing a 1653.7 nm narrow-linewidth distributed-feedback laser source, adopting the multiple reflection chambers and combining wavelength tuning with full digital lock-in amplifier. Using the least squares method, the second harmonic signal data under different temperature and concentrations are fitted. The detection accuracy is improved by taking background subtraction and temperature compensation methods. Experimentally, the low-power on-line system can test the methane gas in full-scope concentration range. It has response time of less than 10 s, and its testing error is lower than ±0.02% under the concentration of 0~1%, and lower than ±2% of actual value under the concentration of 1%~100%. Through the long time stability test and high-low temperature test, high reliability in a wide temperature range (0 ℃~40 ℃) of the system is verified, and the system meets the coal mine test standards and provides guarantee for prevention and control of methane gas outburst hazards.