According to the geological structure and characteristics of seismic activity in the eastern segment of Eurasian seismic zone, China and adjacent regions are chosen as the research regions, where earthquakes of Ms≥60 happened 824 times in total from 1897 to 2008 The sum of the yearly released energy is filtered and studied systematically. The results show that the release of seismic energy features a periodic damped oscillation. Through the oscillation analogy, we can forecast quantitatively the long-term and medium- and short- term seismic situations in China and adjacent regions. Theoretical analysis confirms that the earthquake vibrancy in the continental plates should last 1537 a, namely, 1897—2050 Such a result is consistent with the conclusions from the analysis of Chinese historical seismic data collected for more than 2000 a, and it may be regarded as a theoretical basis that the periodic seismic activity lasts about 150 a in China and adjacent regions. According to the periodic characteristic of the seismic activity, we can forecast theoretically that the current active duration will close in 2010—2012, furthermore, the next active duration will begin near 2020—2021, and then end in 2040 around. Subsequently, the earthquake process will completely enter into a relatively quiet duration for over one century after 2050