Based on the NCEP/NCAR reanalysis data I,the differences in frequency,intensity and related circulation patterns of stratospheric sudden warmings(SSWs) during the past 68 years(1948-2015) were compared.The statistical results showed that 30 SSWs occurred from 1948 to 2015 mainly in cold months from November to March.SSWs occurred more frequently in January and February than in other cold months.In addition,the frequency of SSWs was different from decade to decade.The composite results showed that SSWs in November and December lasted for a longer time than those during January and March.SSWs in March were much weaker and lasted for a shorter period than those in other cold months.The parallel comparison results indicated that the zonal mean signals associated with SSWs in January and March extended downward deeper than those in November,December,and February.The zonal mean signals in November,December,and February could only reach 200 hPa.A negative Western Pacific(WP) pattern was observed one or two weeks before SSWs in all cold months.However,a positive Pacific-North America(PNA) pattern only appeared before SSWs in November,December,and March.Moreover,a negative North Atlantic Oscillation(NAO) pattern was observed one or two weeks after SSWs in November,January,and March.