A　room　temperature　IR　detector　is　designed　by　using　the　principle　of　IR　absorption　gas　directly　absorbing　IR　radiation.　After　the　gas　within　a　closely　sealed　cavity　absorbs　IR　radiation,　the　enlarged　pressure　intensity　within　the　cavity　makes　the　thin　film　deform.　The　size　of　IR　radiation　can　be　measured　from　the　capacitive　variation　quantity　of　a　micro-capacitance　which　uses　the　elastic　thin　film　as　movable　polar　plate.　The　detector　made　with　MEMS　technology　is　sensitive　for　8　-　14　μm　IR　radiation　and　its　sensitivity　≥　2　×　10-3　pF/mW.