Based on the observational data from conventional and automatic weather stations and numerical forecast products of the mesoscale model MM5, the synoptic system and wind field structure of a storm surge in the Bohai Sea on 11 October 2003 were analyzed. The results show that the main causes of the storm surge are the strong northeast wind engendered by strong cold air from northeast and warm air from southwest and inversion; the inshore transport of seawater lasted 10-12 hours over an area of 100 km, directly resulted from the inshore wind and astronomical tides concurrently. It is also found that the occurrence frequency of storm surges has increased obviously since 1985.