Abstract: In the report， the daily ground observation data of Hainan island 18 national meteorological observation stations， NCEP/NCAR monthly reanalysis data， NOAA surface temperature data and climate system monitoring index set of National Climate Centre during 1980 to 2020 were used to analyze the temporal and spatial distribution characteristics of winter fog days in Hainan island and the ocean-atmosphere background characteristics in anomalous years. The results indicated that （1） the high-value areas of winter fog days in Hainan island are concentrated in the northern and central inland areas， the low-value areas are distributed over the coastal areas of southeast and southwest areas. The winter fog days show a significant decreasing trend during the past 40 years， and which is in the less period since 2000，the higher average daily minimum temperature and the increase of average wind speed in winter are the main reasons for the less fog days in winter. （2） In the years of more winter fog days， the western Pacific subtropical high in the interannual scale is bigger， stronger and more westerly； the Southern Oscillation is in negative phase， the sea level pressure in southern areas of China is higher； Hainan island and the South China Sea area show significant convergence at 200hPa， corresponding to the subsidence movement over Hainan island； In the lower and surface layers， Hainan island is located on the northwest side of the abnormally cold high pressure， and are both affected by abnormally southwest warm and wet airflow， the wind s peed are both smaller， the relative humidity is slightly larger， the diffusion condition is worse， which are conducive to the generation and maintenance of fog. In the years of less winter fog days， the situation is reversed. （3） Winter fog days are closely related to SST anomalies. The ENSO state， the prophase SST signal of the West Pacific Warm Pool， and the southeast coast of China are important to indicate the occurrence and maintenance of winter fog in Hainan island. The ENSO distribution pattern， the SST of southeast coast of China and the Western Pacific warm pool have good predictive effects on winter fog days in Hainan island， which are one season， three seasons and one season in advance respectively.