Quick,　accurate　and　reliable　detection　of　mash　gas　plays　an　important　role　in　the　coal　industry.　This　paper　presents　a　novel　method　to　get　the　infrared　absorption　peak　wavelength　by　light　splitting　using　plane　blazed　grating,　instead　of　using　filter　conventionally.　The　principle　and　setup　of　producing　3.433　mu　m　and　4.65　mu　m　wavelength　lights　for　detecting　CH4　and　CO　concentration　are　described　in　details.　The　work　provides　a　simple,　but　efficient　option　to　the　infrared　absorption　gas　detection　technology.