Abstract: In this paper, traditional light interference methane sensor is improved. The light system is simplified, adding the optical-electrical conversion part. It is suitable for intelligent detecting instrument design requirements. On the basis of the theory of wave optics, this paper deduces the relationship between interference fringe intensity and optical path difference, and the relations of gas refractive index and concentration. Finally, the interference fringes are obtained by simulation calculation. The relationship between gas concentration and refractive index, and the relationship between the change of gas concentration and the intensity of fixed point is verified.