Carbon dioxide (CO2) is not only an important greenhouse gas, but also a harmful asphyxiating gas. Therefore, the development of miniaturized, high-sensitivity concentration sensor of CO2 has great application requirements for detecting atmospheric CO2 by unmanned aerial vehicles, sounding balloons, and monitoring CO2 concentration in space-enclosed environments. An experimented setup based on 2.0 μm tunable semiconductor laser was established for the detection of CO2 concentration. The CO2 absorption line at 4989.97 cm-1 was chosen as the target line, and the CO2 gas sensing was carried out using micro-miniature off-beam quartz enhanced photoacoustic spectroscopy. By detecting the photoacoustic signals of a certain concentration of CO2 at different modulation frequencies and modulation amplitudes, the optimal modulation frequency and modulation amplitude of the system were obtained. The CO2 gas is detected under the optimized parameters, a detection limit of 142 μL/L is achieved, which corresponds to a normalized noise equivalent absorption coefficient of 3.37×10-8cm-1W/Hz1/2.