Abstract: A detailed analysis of the synoptic situation, meteorological fi elds was made to get the features of the boundary layer during the fog events which occurred on December 13-14, 2007 by the observation fi eld data, NCEP’s 2.5°×2.5°NC reanalysis data and GDAS Global 1°×1°meteorological data. The results show that: (1) The presence of inversion layer, even multi-layer inversion throughout the fog events, indicates that the atmosphere is more stable, which was conducive to the convergence of water vapor before fog formation, then not favorable for the divergence of water vapor after fog formation, which helped the development and maintenance of the fog. (2) The water vapor fl ux transported in radiation fog was smaller than the advectionradiation one, and the water vapor in radiation fog was mainly from the local moisture condensation. (3) The surface was dominated by high pressure, during the radiation fog event, the divergence of water vapor fl ux was always positive, indicating that the water vapor near the surface was easy to be held and conducive to radiation cooling during the radiation fog event, while the divergence of water vapor fl ux and the northern cold air made the fog life a little too short.