By using four meteorological stations' data in Zhoushan from 1962 to 2015, the hourly automatic weather observation data and buoy station data from 2014 to 2015,the features of the sea fogs over Zhoushan sea area were statistically analyzed. Results show that the sea fog usually comes with the large scale background condition and a certain hydrographic characteristics. It shows that they come frequently in spring and less in autumn; however, they usually happen in the nighttime and early morning, while the time between midnight and early morning is the most frequently, and the fogs won't lift until 11:00. The sea fogs can be divided into four types on the basis of weather situations, while it has lots of differences for the seasons' changes and diurnal variations. This is the element characteristic of the heavy fog:the air temperature in the range of 5-27℃,the sea surface temperature in the range of 9-27℃,the depression of dew point in the range of 0-4℃. About 90% heavy fogs happen when the relative humidity (2 m highly) ≥ 95% and air-sea temperature difference in the range of -3.7-3.2℃, and the wind direction of the heavy fogs usually land between southeasterly and southerly winds, while the average wind speed in the range of 1-5 gale. By using the element threshold to show the revision of WRF visibility mode,it can obviously improve the accuracy of the qualitative forecasting for the heavy sea fogs.