A carbon dioxide (CO2) sensor is developed using quartz enhanced photoacoustic spectroscopy (QEPAS) with a 2.0 μm distributed feedback diode laser.The detection is based on a 2ｆ wavelength-modulation spectroscopy approach by dithering and scanning the laser current.The laser modulation depth is optimized at normal atmosphere pressure and room temperature.The influence of the H2O presence in the sample gas mixture on the CO2 sensor performance is also investigated.The results show that,with 1% CO2 concentration,the H2O in the concentration ranges of 0 to 0.2% has an effect on the CO2 signal amplitude and phase,and the largest amplitude difference is ~2.1 times.When the H2O concentration is over 0.2%,the CO2 signal amplitude is saturated and remains steady.Atmospheric CO2 concentration is well measured using the optimal sensor parameters.Benefiting from the strong absorption line intensity at 4 989.97 cm-1,a detection limit of 19 ppm (1σ,300 ms averaging time) is achieved,which corresponds to a normalized noise equivalent absorption coefficient of 4.71×10-9 cm-1·W·Hz-1/2.