CO2 in a closed environment can lead to safety problems such as suffocation. Therefore, the development of miniaturized and highly sensitive CO2 detection technology has important significance and application requirements in the detection of atmospheric environment and safety monitoring of closed environmental work areas. In this paper, based on the rapid development of miniaturized quartz-enhanced photoacoustic spectroscopy technology, the research on CO2 detection has been carried out with a relatively simple off-beam structure scheme. Off-beam quartz-enhanced photoacoustic spectroscopy has the advantages of small size, high sensitivity, anti-interference, low cost, low power consumption and low laser requirements, and has great potential for developing low-power portable gas sensors. In recent years, especially with the gradual maturity of near-infrared laser technology, it provides better quality and higher energy excitation light source for this technology, Off-beam quartz-enhanced photoacoustic spectroscopy has a higher detection sensitivity and enables accurate detection of low concentration gases. The HITRAN database 2012 is used to screen out the suitable absorption line (at 4 989.97 cm-1), and the 2.004 μm near-infrared distributed feedback semiconductor laser is selected as the excitation source. The CO2 photoacoustic signal is excited by the wavelength modulation method, and the second harmonic detection technology is used to detect the photoacoustic signal. In the experiment, the detection performance is improved by humidifying the injected carbon dioxide gas and optimizing the modulation amplitude, and the detection of air CO2 is realized. Under normal pressure, different concentrations of CO2 samples are arranged by gas distribution machine, and the response characteristics of concentration and signal are studied by preparing different concentrations of CO2 samples thought gas distribution machine, and a good linear response result is obtained. At the same time, the signal offixed concentration of CO2 sample under different pressures is measured, and Allan variance was used to evaluate the system performance. The results show that when the average time is 1 000 s, the detection limit of the system is 4×10-3 μL·L-1. The best 2f signal is obtained at a pressure of 150 Torr. The minimum detection sensitivity of the system for CO2 is 15 μL·L-1 at atmospheric pressure, and it is reduced to 6 μL·L-1 at 150 Torr.