In order to accurately measure the concentration of NO2 gas by mid-infrared differential absorption lidar, the absorption spectrum characteristics of NO2 in mid-infrared band were measured and analyzed. The absorption cell experiments were conducted using two wavelengths λon and λoff emitted from OPA lasers and OPO lasers respectively. The absorption cross section of NO2 gas in the range of 3 410~3 433 nm is measured by a laser λon whose spectral line-width is less than 0.05 nm. The absorption cross sections at 291 K, 308 K and 363 K were acquired respectively. And the absorption spectra from 3 400~3 435 nm were also acquired by a laser λoff with spectral line-width being 10 nm. The experimental results show that the absorption cross-section is negatively correlated with temperature in the range of 3 410~3 433 nm, consisted with HITRAN database and the correlation coefficient between the measured data and the HITRAN data is above 0.92. A new convolution correction method is used to calculate the absorption spectrum line under laser λoff. The correlation coefficient between the measured results and the fitting results is 0.97. The measured absorption cross sections at the on and off wavelengths are applied to the simulation of the mid-infrared differential absorption lidar, the concentration error of differential absorption lidar is simulated, which verified the feasibility of the scheme of differential absorption lidar.