The dynamic and thermal features of a rare radiation & advection fog in Dalian that occurred during 30 November and 2 December 2009 are analyzed by using the station observation data in Dalian Airport, sounding data, convection data of MICAPS and NCEP/NCAR reanalysis data.The results show that the heavy fog was of radiation & advection type and it occurred in the stable stratification in large scale circulation; the sounding data showed that single or multiple thermal inversion layers occurred in the fog process.The temperature inversion and sufficient vapor were very important for the formation and maintenance of the fog.Analysis of the thermal fields showed that a cooling process produced by net surface radiation fluxes played a key role in the fog.The continuous weak warm and moist advection on lower layers led to the formation and maintenance of the temperature inversion on this layer.Analysis of the dynamic fields showed that the situation of weak convergence and the slightly upward vertical velocity occurred at the beginning and during the maintenance of the fog on the low-altitude layer while weak divergence and the slightly downward vertical velocity occurred during dissipation time.Analysis of the vapor condition showed that reinforcing the humidity and cooling the temperature were both important in the process of bringing in enough vapor to be saturation.Weak convergence of vapor occurred at the beginning of the fog while weak divergence existed during the dissipation time.