The invention belongs to the technical field of thermopile infrared gas detectors, and particularly relates to a thermopile infrared gas detector taking a composite film as an infrared absorption layer, and a processing method of the detector. The detector and the processing method solve the problems that the traditional thermopile infrared detector is low in thermoelectricity conversion rate and a suspension structure is damaged easily during a release course. The detector comprises an SOI (silicon on insulator) substrate, thermocouple strips, an SiO2 dielectric layer, metal connection and welding discs, SiO2 isolation layers and an absorption layer, wherein cold ends of the N/P polycrystalline silicon thermocouple strips are supported with the SOI substrate, and the absorption layer is arranged at the top of the detector in a suspension manner. According to the detector and the processing method, a higher absorption rate of the composite nano film to a near-infrared band is utilized, and the absorption layer is suspended above the detector, so that a unit duty ratio of the detector is increased, response and detection rates of the detector are increased correspondingly, and a performance index of the detector is optimized.