A spectral imaging system based on acousto-optic tunable filter (AOTF) was designed and built. The system consists of a front imaging lens, an AOTF, a relay objective, a CCD camera, an AOTF radio frequency driver, and a host computer. It can scan the wavelength of diffracted light from AOTF, and collects spectral images using a CCD camera, ultimately generating a spectral image cube. The system can be applied in the range of 400–700 nm, with spectral resolution better than 1 nm, and it has no scanning mechanical structure and realizes the integration of image and spectrum. Field imaging experiments were carried out using this system, and the imaging result after being processed using the suppression method for 0-order light interference were clear and recognizable. Furthermore, the system was used to measure different NO₂ sample gases with given concentrations from 3.62 × 10¹⁷–1.21 × 10¹⁹ molecule/cm². The measured spectral data were retrieved by differential absorption spectrum algorithm to obtain the measured concentrations of NO₂ sample gases. The error and correlation between the measured values and the given values were analyzed. It is shown that the errors are within 20% and the correlation coefficient of 0.99401, indicating a good correlation between the measured values and the given values, which verifies the feasibility of the system in pollution gas measurement.