The basic principles of photoacoustic spectroscopy were introduced. A portable photoacoustic spectroscopy system Transport-X, which can detect a series of DGA products developed by Kelman Company, was applied to detect CO and SO2 of SF6 decomposition. The filter of SO2 was selected according to the HITRAN2004 database as a result of the incapable of detecting SO2 of Transport-X. One of the filters of Kelman was replaced by the new selected SO2 filter. Calibration experiments of different concentrations of CO and SO2 were carried out and the results showed that photoacoustic signal and the concentration have a perfect linear relationship and the detection limit for CO and SO2 are 4.063 ppm and 9.540 ppm.