Using the ground observation data of Xuwen National Meteorological Observing Station from 1990 to 2023 and the NCEP/NCAR reanalysis data, the characteristics of climate change, meteorological elements and common synoptic situations of the occurrence of dense fog in the Qiongzhou Strait are statistically analyzed. The results are shown below. (1) The annual average number of foggy days in the Qiongzhou Strait is 16.6 d, and the interannual change of foggy days presents a decreasing trend. Winter is the season with the highest frequency of dense fog in the Qiongzhou Strait, accounting for 51.8% of the annual total number of dense fog days, while summer sees the lowest frequency, making up only 7.8%. February is the month with the most dense fog days in the Qiongzhou Strait with an average of 4.2 d, accounting for 25.3% of the annual total number of dense fog days, while July has the least average number of dense fog days (only 0.3 d). The dense fog in the Qiongzhou Strait mainly occurs from 04:00 to 08:00, accounting for 42.7% of the whole day; the peak appears at 06:00, and the valley at 13:00. (2) The ideal meteorological conditions for the formation of dense fog in the Qiongzhou Strait are as follows: the easterly wind (ENE-ESE) prevails on the surface with the wind speed concentrated in the range of [1.0，5.0) m·s-1, the temperature is in the range of [16，22) ℃, the depression of the dew point (t-t_d) does not exceed 2.0 ℃, the pressure is in the range of [1 005.0，1 017.5] hPa at the station, and the relative humidity is higher than 90%. (3) The circulation patterns of the fog in the Qiongzhou Strait can be divided into 5 types: the front low pressure, the high pressure entering the sea, the stationary front, the front of cold front and the equal pressure field, which account for 10.8%, 13.5%, 21.6%, 24.3% and 29.8%, respectively. Among them, the front low pressure type and the high pressure entering the sea type mainly produce advection fog, the stationary front type often produces mixing fog, the front of cold front type produces frontal fog and the equal pressure field type mainly produces radiation fog. The 5 types of weather patterns and the fog types they generate provide reference for practical operations.