Abstract: Using the conventional meteorological data, ERA5 reanalysis data, and pollutant concentration data, the characteristics and causes of a sustained haze in Dazhou in January 2023 were analyzed. The results showed that: (1) The configuration of high-altitude meridional circulation, low-level weak warm advection, and ground pressure field in the early stage provided favorable circulation background for the formation and maintenance of haze weather. In the later stage, the southern trough became active, the water vapor conditions improved, and there was weak precipitation, which was conducive to the maintenance of heavy fog or fog and the accumulation of pollutants, and the haze weakened and disappeared. (2) The boundary layer inversion was an important feature of the haze process, and the formation and maintenance of haze were positively correlated with the inversion intensity (especially the double-layer strong inversion). The high wet layer thickness was beneficial for maintaining heavy fog or fog and increasing the moisture absorption of pollutant particles, but was not conducive to maintaining haze. (3) Weak wind conditions, weak negative vorticity (or zero vorticity) in the lower layers, and weak turbulent motion in the boundary layer were conducive to the formation and maintenance of haze.