Abstract: Inappropriate description of physical processes within the boundary layer and errors in the initial condition are two primary reasons for the low accuracy of sea fog simulation. In order to obtain more satellite data assimilation and simulation experience for improving the initial condition, the present paper investigates the impact of assimilation of FY-3A MicroWave Humidity Sounding (MWHS) and MicroWave Temperature Sounding (MWTS) data derived from optimal channels. The WRF-3DVar (Weather Research and Forecasting-Three-dimensional variational data assimilation) is applied to assimilate these data that have been quality controlled and bias corrected in simulation and prediction experiments of sea fog over the Yellow Sea and Bohai. Analysis of the increments of temperature and relative humidity from the assimilation system over the sea fog region detected by Geo-satellite indicates that differences in the model capability for sea fog simulation and various types of sea fog that are related to the environmental condition have significant influences on the assimilation effects, i.e. the model performance is greatly improved by assimilation for the simulation of cold-type advection sea fog, which the model already has a strong simulation ability. However, for warm-type sea fog that involves non-typical mixing processes, data assimilation results in little changes in the simulation. In order to determine the reasons, direct comparisons between the simulated temperature and relative humidity at a sea fog covered grid and standard rawinsonde observations nearby, and analysis of the evolution of the temperature and relative humidity and their increments from assimilation at all sea fog covered grids, are carried out. The results show that the increments from assimilation at the cold-type sea fog covered grids can make up the deviations between observations and simulation by reducing temperature and increasing relative humidity; meanwhile, the atmospheric water vapor and liquid water contents also appear to be adjusted by assimilation. Possible increments and adjustment in the boundary layer by assimilation are also found in the vertical direction. However, similar phenomena and other beneficial signs of adjustment are not found during the warm-type sea fog period.