The invention belongs to a quick-response infrared gas senor with high sensitivity within the range of an explosion-proof air detecting device for mine safety. The absorbing cavity of the infrared gas senor is characterized in that a plane reflecting mirror and a concave spherical reflecting mirror form a quasi-optics resonate cavity, a light source and a detector are fixed on one side of the plane reflecting mirror, and light source position and detector position are in mutual conjugation and fixed by a bracket; the concave spherical reflecting mirror is fixed on the upper part of the sensorhousing, and the bracket and the sensor housing are fixed on the base. The air absorbing cavity of the invention adopts quasi-optics resonate cavity design to enable the light source and the detectorto correspond with imaging relationship after multiple light path folding, a beam imaged on the detector is in dispersion, so that the beam is evenly distributed, and the noise-signal ratio of the optical signal is improved. The invention not only reduces the volume of the absorbing cavity, but also improves the absorbing effect of tested air to light; thus, the invention satisfies the requirement of the quick-response infrared gas senor with high sensitivity.