On the base of meeting requirements of gas detection, a low-cost, low-power, low limit of detection, high SNR(signal to noise ratio) pocket methane detector was designed, with the improvement on the original gas absorption theory, and the core sensing module contains a mid-infrared light source, optical path, a mid-infrared dual detector. The device adopted dry batteries single power supply, and totally the supply current was less than 150 mA while the power consumption was less than 0.9 W, and the gain of the circuit was 43.3 dB. The single and dual channel detection experiments were carried out to contrast, and with the novel proportioning gas method both the sensitivity and the minimum detection limit under low concentration range could reach to 50 parts per million. Compared with the pre-existing wall-mounted devices, this device satisfies the requirement of detecting explosive gases in a more convenient handheld style.