The airborne imaging DOAS (differential optical absorption spectroscopy) method which can obtain two-dimensional distributions of trace gas is introduced in this paper. Based on this method, pollution source in a wide range of area can be found quickly, and a map of trace gas distribution can be obtained to study the pollutant diffusion tendency. In this paper we report the flying experiment over Tianjin and Tangshan. The airborne imaging system is introduced in detail and an image of two-dimensional NO2 distributions is obtained with a resolution of about 30 m×80 m. Combined with wind field data, the emission rate of a point source on the flight path is calculated to be 1570 kg/h.