CO is an important product of partial discharge fault in SF6 and C5F10O gas-insulated equipment, and the high sensitivity detection of CO is helpful for the safe operation of SF6 gas-insulated equipment. Therefore, the photoacoustic spectroscopy of CO was studied by a near-infrared distributed feedback laser diode (DFB) with a central wavelength of 1567 nm combined with Erbium-doped fiber amplifier (EDFA) with a saturated output power of 2 W. The basic principle of photoacoustic spectroscopy detection is analyzed and the sound pressure distribution and resonance frequency of the photoacoustic cell with a length of 95 mm and a radius of 5 mm are simulated. Using wavelength modulation technology, the second harmonic signal of multi-concentration CO was studied under the optimal modulation depth and modulation frequency. The results of the second harmonic detection show that the lower detection limit and linear correlation of the system is 65.7 ppm and 0.996, respectively.