The invention belongs to the technical field of optical fiber sensing and trace gas detection, and relates to a poly(monochloro-p-xylene)-based membrane resonance type gas sensor and a detection system. The gas sensor adopts a structure of an F-P interferometer; and an F-P cavity of the F-P interferometer is also a non-resonance photoacoustic tank a photoacoustic system. Parylene-C has relativelylow young modulus and relatively large elongation at break, so that a Parylene-C membrane prepared through a vacuum vapor phase polymerization deposition has the characteristics of strong coating property and high deposition uniformity; therefore Parylene-C membrane prepared through the vacuum vapor phase polymerization deposition has the characteristics of large radius and thin thickness. The inherent resonance frequency of the F-P interferometer is in direct proportion to the thickness of the diaphragm and is inversely proportional to the square of the radius of the diaphragm, so that the resonance frequency of the F-P interferometer can be as low as several tens of hertz. The invention provides a novel technical means for high-sensitivity long-distance gas telemetering in a narrow space.