In order to realize the high precision detection of the volume fraction of methane,the photonic spin Hall effect phenomenon with high-quality factor is excited by a multilayer structure.In an asymmetric arrangement,a methane-sensitive film was introduced into the structure,and the volume fraction of methane could be detected by the change in the refractive index of the sensitive film.The effects of gas porosity,period number,metal thickness,and sensitive film thickness on the photon spin Hall effect were studied,and the transfer matrix method was used for numerical analysis.The results show that the sensor can detect methane gas with volume fraction of 0~ 3% (refractive index change is 1.4364~ 1.4478) with a sensitivity of 29.6°.The highest figure of merit and the lowest detection limit are 395 and 0.00012,respectively.The sensor has a simple structure and strong detection ability,which provides a new idea for the research of optical sensors.