Abstract: In order to monitor SF₆ gas concentration in electric power site effectively, based on wavelength tunable CO₂ laser, a set of SF₆ trace gas detection system under atmospheric environment was designed by means of photoacoustic spectroscopy gas detection technology. Differential photoacoustic spectroscopy technique was proposed to improve detection sensitivity of photoacoustic system. The results show that resonant center frequency of the designed SF₆ gas detection photoacoustic system is 1066Hz, quality factor is 32.04 and photoacoustic pool constant is 89.74 Pa·m·W^-1. Sensitivity of SF₆ gas detection at laser spectral line 10P12 is 0.06×10^-6(volume fraction) by using single spectrum photoacoustic method. Sensitivity of photoacoustic system at 10P12 and 10P16 and at 3W modulated light increases to 0.02×10^-6(volume fraction) after using differential photoacoustic spectroscopy gas technology. Differential photoacoustic spectroscopy can effectively reduce noise effect and enhance the sensitivity of photoacoustic detection system. It has practical value.