In this paper, using the automatic station, microwave radiometer and wind profile radar data of Xiang 'an, Xiamen, from March 30 to April 3, 2021, a fog process lasting for 5 days on the west coast of the strait was studied, the boundary layer characteristics of the fog were analyzed. The study found that: there was weak precipitation in the fog development process, and the precipitation strengthened the fog; The existence of inversion layer is an important condition for maintaining fog, and the weakening of inversion layer will weaken or even dissipate fog. There are two phenomena in the decrease of the inversion layer thickness. One is that the top height of the inversion layer remains basically unchanged and the bottom of the inversion layer rises, and the other is that both the bottom and the bottom of the inversion layer rise upward, which is related to the change of atmospheric temperature near the top of the inversion layer. The former makes the inversion intensity weaken, and the latter makes the inversion layer disappear and the fog dissipates. The southwest wind brings warm and wet air, which provides water vapor conditions for the formation of fog. When water vapor is abundant on the ground, the strong updraft will lift the fog to form stratiform clouds, and the water vapor will accumulate to a certain extent to form precipitation. On the one hand, the precipitation in the fog process causes the evaporation of water on the ground, which provides conditions for the intensification of fog or the generation of the next precipitation. On the other hand, it consumes water vapor in the air and accelerates the dissipation of fog. There were three large jumps of liquid water content in the fog process, which occurred above the inversion top, and precipitation occurred after the liquid water jump.