By using conventional observation data and NCEP reanalysis data, a sustained fog and haze event that occurred in Jiangsu Province in early and middle June was analyzed from several perspectives including pollution, circulation background, surface meteorological characteristics, and vapor, thermal, and dynamic conditions. The results showed that the residue of crop-burning, which caused a large aerosol burden, was the main reason for the sustained haze, whereas the heavy fog was formed mainly by radiation and advection inversions. The aerosol particles also provided condensation nuclei for fog formation. High-level cold air did not completely dissolve the underlying relatively stable stratification. Lower wind speed and higher relative humidity of less than 3 m/s and greater than 80%, respectively, were shown to be favorable for the development of the fog and haze. Frequent weak precipitation processes also played an important role in the fog formation and aggravated the haze conditions. The maintenance of near-surface temperature inversion or nearly neutral stratification provided favorable stratification conditions for the persistence of the fog and haze. Moreover, a strong correlation was present between vertical upward movement and haze development. Underlying weak upward motion with specific moisture conditions was conducive to the upward development of the mist. By using backward trajectory simulation, the authors determined that in addition to local suspended particulate matter, the pollutant transport from Anhui Province was an important factor for the sustained fog and haze. In the northern regions, local pollution sources were the main factors.