Abstract: The safety CH4 opticalfiber sensor is studied based on the optoelectronic measurement theory and wavelengthdivision multiplexer technology. By use of the CH4, the sensor of the system works in the harmonic absorption spectrum at 1.331μm. The system works in dualwavelength differential absorption mode and its reference wavelength is 1.27μm, so the effect of the dispersion and perturbation , except the light absorption, is eliminated. The resolution of the system has reached 0.001% and the realtime display has been realized by the data acquisition and processing with A/D/A conversion card controlled by the software. The system may not only be used to accurately measure CH4, but also to operate safely and reliably because of the application of the optical measurement. Therefore, the system can be used for any coal mine to measure the concentration of CH4 in remote supervisory control mode.