Abstract: The intraseasonal oscillation features of 30 hPa height field in the Northern Hemisphere from 1 Jan. to 31 Dec. 1975 are investigated by using Singular Spectrum Analysis (SSA). The results show that there is remarkable intraseasonal oscillation in which the period of 20 to 60 days is predominant in addition to annual variation and seasonal cycle in lower stratosphere. The 20 to 40-day periodic oscillation of the height variations at 30 hPa prevails in the frequent occurrence area of persistent anomalies, while 40 to 60 days periodic oscillation in other areas. The persistent anomalies are mainly related to the 20~40 days oscillation in troposphere and likely to affect the intraseasonal variation in lower stratosphere via the interaction between the oscillations in both troposphere and stratosphere.