The weather system which caused strong winds in Bohai Sea and Yellow S ea from 1987 to 2006 was analyzed by using the NCEP reanalysis data of 500hPa he ight and sea surface pressure distribution, the in situ ground observations in th e costal areas, oil platforms in the sea, islands and ship reports. Also the sta tistical data of fishery boat windage loss accidents from Analysis Report of Chi na Fishery Vessel Safety (1999-2005) were used. The conclusions are in the following. (1) In winter the number of cold air from the northwest direct ion was in the majority and accounted for 50.4 percent of total amount. (2) Among the weather system which caused strong winds in Bohai Sea and Yellow Sea, the nu mber of small trough developing type was 112, which was 50.0 percent of total number. And the number of the turning type from zonal to meridional direction was 61, which was 27.2 percent of total amoun t. (3) The frequency of cold air outbreak process in winter dropped in the last 20 years. (4) The number of windage loss accidents occupied 51.85% of the total n umber of fishery boat loss accidents. And the sudden strong winds in winter were the main causes that led to wooden fishery boat windage loss.