Abstract：Based on the observation and numerical simulation of visibility in Bohai Sea and its west coast from December 1， 2019 to November 30， 2020. This paper studied the evolution characteristics and prediction methods of visibility in this region. The study showed that there were differences in the evolution characteristics of visibility between the Bohai Sea and the west coast of Bohai Sea. The visibility of the sea （including ports） was higher than that of the land， and daily variation of visibility on the former was more gradual than on the latter. The low visibility weather （< 3 km） mainly occursed on land from 0：00 to 8：00， while the sea （including ports） may occur all day. The low visibility weather at sea （including ports） was more than that on land from 0 to 500 m.The low visibility weather from 500 m to 3000 m was less than that on land. The visibility forecast in Bohai Sea and its west coast needed to consider the influence of aerosol enction. The correlation coefficient between observation and numerical simulation by ECMWF about visibility prediction was 0.2~0.3，and the relative error was 40%~50%. PM2.5 mass concentration forecast by Tianjin environmental model was introduced. Based on relative humidity by ECMWF model and liquid water content by environmental model， The extinction equation could be used to improve the visibility forecast in this area. The correlation coefficients between the visibility forecast and the actual situation on land and port were above 0.8 and 0.5， and the relative errors were about 20% and 40%. The forecast accuracy was 50% （hours less than 3 km）， and the daily minimum visibility was less than 70%， which was one third lower than that on land at sea. Based on the air-sea coupling technology and aerosol assimilation technology， the visibility prediction ability at sea and on land could be further improved. The winter experiment showed that by adding the regional air-sea coupling model and aerosol three-dimensional variational technology， the correlation coefficient between visibility prediction and actual visibility in Bohai Sea could reach 0.72， and the relative error was reduced to 26.0%， while the correlation coefficient between land visibility prediction and actual visibility was 0.95， and the relative error was 15.5%.