Based on the data of automatic weather station, windprofiling radar, ERA5 reanalysis, Himawari 8 high resolution satellite and FM120 fog droplet spectrometer, we discuss the circulation pattern and microphysical characteristics of an sea fog event that happened in southern coastal area of Fujian Province on 7 April 2019. Circulation analysis shows that this sea fog event occurred under the control of westtonorthwest flow at 500 hPa trough bottom, while from 700 hPa to surface there was uniform southerly flow. The sounding situation was stable. Before sea fog event, lowlevel wind speed decreased significantly, increasing the thickness of lowwind speed. This situation provided stable circulation for sea fog. Himawari 8 satellite images show that the sea fog rapidly formed in the Taiwan Strait first and then advected to coastal area affected by lowlevel southerly airflow. Hydrological analysis indicates that there existed a cold water band and large temperature gradient near the shore. Sea surface temperature (SST) varied between 18 ℃ and 24 ℃. The air and sea temperature difference was between 0 ℃-2 ℃ with sea surface colder than the air above, which contributed to the formation of advective sea fog. Fog droplet spectrum analysis shows that visibility decreased dramatically while particle number concentration (PNC), liquid water content (LWC) and droplet spectrum increased significantly at the same time. During the sea fog process, 5 min average PNC exceeded 200 cm-3 and instantaneously reached 468 cm-3 maximum, and the average PNC during the fog process reached 100 cm-3. The 5 min average LWC reached 0.41 g·m-3 and 1.35 g·m-3 instantaneously. The average LWC during the fog process reached 0.17 g·m-3. Fog droplet size featured double peaks with 4-6 μm and 22-26 μm intervals respectively during the fog process. This indicates that small and big particles both can contribute to the formation of sea fog. 