The dual-channel non-spectroscopic infrared gas detection method is adopted, and the traditional infrared gas absorption theory is modified to develop a handheld infrared methane detector with low detection limit and high detection performance. Through the light simulation software TracePro, a variety of optical path structures were compared to obtain the long-path gas chamber structure in a small space to enhance the effective absorption of gas and improve the detection performance of the instrument. The multi-parameter compensation algorithm is introduced to optimize the Lambert-Beer law, and the gas absorption function adapted to the detection system is obtained to ensure the accuracy of the calculation of gas concentration information. When the instrument works, the maximum output current is 130 mA, which is powered by dry battery. The size of the instrument is 209 mm×70 mm×40 mm. The minimum detection limit is below the explosion limit of methane gas concentration reaching to 50 ppm, which can ensure the safety of the gas against explosion.