In this paper, a differential measurement system of methane concentration by using LED as the light source is reported. The functions of each optical element in the system are carefully analyzed, and the calculation method and the experimental results of methane concentration are given. The R branch in 2ν_3 spectral band are selected as the working spectral lines. A Fabry-Perot interferometer is used,and the transmission curve of the interferometer matches the absorption peaks of the methane at the working spectral lines.So that the useless light from the light source can be filtered out. The cavity length F-P interferometer is modulated by PZT, and the differential absorption measurement is realized. In this way, the measurement sensitivity is enhanced and a good result has been achieved.