A photoacoustic spectroscopy detection system based on a broadband light source is introduced, and the methane concentration is detected at the optimum modulation frequency of 22 Hz; further, the stability and the minimum detection concentration of the system are analyzed with Allan variance. The research results exhibit that the concentration (volume ratio) detection limit of methane can exceed 1 × 10 -6. The methane concentration is detected by broadband photoacoustic system and direct absorption detection system based on distributed feedback diode laser source with a long path absorption cell simultaneously. The detected results show that the error of methane concentration detection by the broadband photoacoustic system is about 8%.