Based on hourly ground conventional observation data, L-band sounding data, wind profile radar data, Himawari satellite data from Japan and ERA-Interim reanalysis data, the characteristics of a persistent sea fog process from 15 to 25 February 2018 over the Qiongzhou Strait were analyzed. The results show that the persistent sea fog process was divided into four stages and three types, including radiation fog from 15 to 17 February, advection fog from 18 to 20 and 24 to 25 February and frontal fog on 22 February, respectively. During the radiation fog, the circulation situation of pressure field over the Qiongzhou Strait was uniform, the air temperature dropped and the water vapor was saturated at night, and the double-layer inversion appeared below 1000 m, the fog top appeared at the bottom of the first inversion layer. During two advection fogs, the stronger east-southeast airflow at the back of denatured high pressure ridge entering sea controlled the Qiongzhou Strait, and the temperature (relative humidity) kept constant (saturated) for a long time. Compared with the advection fog from 24 to 25 February, the low-level wet advection of advection fog from 18 to 20 February was stronger, the water vapor convergence layer was thicker, and the specific humidity increased persistently, which were conducive to its persistence for the long time. The larger vertical wind shear below 600 m mixed the air evenly, and the fog top reached 1000 m and above. During the frontal fog, the wind speed of northerly wind exceeded 4 m·s-1 at Xuwen station, and accompanied by weak precipitation. The center of wet advection (water vapor convergence) and the frontal area of intersection between cold and warm advection located at lower layer near the Qiongzhou Strait. In each stage of sea fog, the air-sea temperature differences were -2 to 3 ℃. When the temperature difference increased, the sea fog dissipated.
