From April 10 to 14,2022, a long-duration, wide-range and high-concentration sea fog event occurred in the coastal waters of Zhejiang Province. In this paper, the characteristics and causes are analyzed by using satellite data, ERA Interim reanalysis data and Zhejiang coastal automatic station observation data. The results show that the inversion layer makes it difficult for the low-level water vapor to spread to the upper air, which is conducive to the generation and maintenance of fog. In the fog formation stage, there is obvious water vapor convergence, at the same time, the temperature is higher than SST and the difference is 0-2 °C. In the maintenance stage, water vapor convergence gradually weakened， the air-sea temperature difference is basically around 0 °C. In the dissipation stage, there is obvious water vapor divergence ; the air-sea temperature difference is greater than 2 °C or less than 0 °C.