Quartz enhanced photoacoustic spectroscopy (QEPAS) has the advantages of high sensitivity, good reliability and small system volume in the detection of trace gas concentration. Taking carbon dioxide (CO2) as the target gas, the influence of different gas flow rates on the accuracy of qepas detection system was studied. The flow field of gas is analyzed by fluent ANSYS simulation software, and the simulation of pressure and velocity in the air chamber is completed by simulation software. The influence of gas chamber pressure on gas concentration detection is studied by the experiment of CO2 gas detection system based on QEPAS. The experimental results show that when the pressure in the gas chamber is 1.08e-1~1.48e-1 Pa by controlling the gas flow, the linear relationship between the detection signal and the gas concentration is great, the correlation coefficient R = 0.99971, the relative error of the system is 0.5%, and the detection limit of the system is 72ppm.