Based on the air pollution monitoring data, meteorological observation data, NOAA monthly mean Arctic oscillation (AO) index and ERA5 reanalysis data in January from 2013 to 2020, the meteorological causes of more haze days in Hohhot of Inner Mongolia in January 2020 were analyzed. The results are as follows: (1) The weak winter monsoon circulation, the atmosphere with high humidity, low boundary layer and inversion structure in January 2020 were the main reasons of more haze days. (2) There was a significantly positive correlation between daily average relative humidity, accumulated precipitation, the number of days with 2 min average wind speed per hour equal to or less than 1.5 m·s^-1 and haze days in Hohhot in January from 2013 to 2020, among which the 2 min average wind speed per hour equal to or less than 1.0 m·s^-1 was more conducive to the occurrence of fog and haze. (3) Surface snow cover had a great influence on the continuous haze event. The deeper and longer the snow cover lasted, the more haze days were in January in Hohhot. (4) When the haze weather continued in Hohhot in January 2020, the average height of the boundary layer was about 430-550 m, with the lowest of 210 m. The lower boundary layer contributed to the accumulation of pollutants near surface layer, leading to the deterioration of visibility. The lower the boundary layer height was, the heavier the pollution would be.