Based on the theory of infrared absorption, a new kind of portable methane alarming device has been developed with the advantages that cost-low, maintenance-free, miniaturization, and integration. Intrinsically safe circuit is absolutely necessary, because the device is installed in the explosive gas environment. To improve the detection accuracy and increase the safety of the coal mine, the device’s intrinsically safe circuit has been designed. All parameters of the circuit are designed in accordance with IEC 60079-0-2007 Explosive atmospheres-Part 0: Equipment - General requirements and IEC 60079-11-2006 Explosive atmospheres-Part 11: Equipment protection by intrinsic safety “i”. The related analyses and calculation results show that this intrinsically safe circuit is workable and reliable.