Based on hourly ground observation data, daily sounding data for every 50 m at 08:00 and 20:00 BT in Minqin Weather Station, and the NECP reanalysis data, a rarelyseen heavy fog process in Minqin from 9 to 13 November 2015 is analyzed. The results show that the increased ground relative humidity after preprecipitation provided necessary moisture condition, stable high and lowlevel circulation configurations provided a stable stratification and light wind condition for the fog formation. The thickness and intensity of fog layer were closely related to the thickness and intensity of inversion layer near surface, boundary layer height, vertical movement of moisture and absolute value of (Ts-Ta) over night. The higher the boundary layer, the thicker the inversion layer near surface, and the thicker the fog layer. The more intensive the inversion layer, the smaller the absolute value of (Ts-Ta) at night, and the more intensive the fog layer. The stable highlevel circulation, intensive inversion layer and stable isothermal layer near surface and the longlasting saturated moist layer contributed to the rarelyseen intensity and duration of the heavy fog process this time.