Abstract: Based on sea level pressure data from 1873 to 1990, the East-Asian monsoon inten-sity index is caculated to discuss the periodic oscillation of East-Asian monso on long-term variation in recent century by using the method of singular spectral analysis (SSA). The results indicate that the long-term variation in East-Asian monso on shows the interannual oscillation of the quasi-biennial (QBO) and 3-6 years (LFO) and the interdecadal oscillation of 16-18 years (IDO); that these oscillation components exhibit the interdecadal variation, and the QBO is remarkable especially; that the amplitude of QBO in winter monsoon is smaller before 1920s and shows the wavelike changing with greater amplitude of about 12 years and smaller of about 6 years; that the summer monsoon changing is opposite to winter monsoon with about 6 years greater and about 3 years smaller; and that the interdecadal variation in summer monsoon is dominant.