Gas monitoring for methane concentration has been applied in many areas, while the vast majority of methods were based on the chemical reaction. There is a low security and poor stability shortcomings. In contrast, it is of high stability and strong anti-interference ability to monitor methane concentration using optical interferometry for quantitative analysis. As the system static interference limits the spectrcum resolution, we designed the electro-optical modulation interference system to further improve the detection accuracy for methane concentration. In the interferometer system, a variable refractive index crystal LiNbO3 was used for electro-optical modulation, and the static optical path length scan range was increased to improve the spectrum resolution. Both sides of the crystal were loaded with opposite phase modulated signal, so that it does not change the improved spectrum resolution interferometer size. By derivation of refractive index modulation as a function of optical path difference, the simulation found that the resolution was increased by nearly an order of magnitude than interference system spectrum resolution of the same size. The experiments used the SGT-3-type acousto-optical modulator and the 1 650 nm infrared lasers to detect different concentrations of methane gas. The experimental results show that the method is better than the traditional pyroelectric method in terms of accuracy and stability, and more suitable for application in the mine complex environment.