Abstract: According to the stratification and the ordering of seismicity, the time structure of earthquakes which M≥7 in China continent and its adjacency has been analysed and the grouping regularity of large earthquakes within these seismic episodes has been studied as well.The three criteria of seismic active episode, i.e., high magnitude(Ma≥7(1/2)), short period(△t<6 years) and small K value(K<10), has been given.Also, from the parameter values of a strong earthquake grou pwithin a tranquil episode, we can judge the time commencement of the first large earthquake in the next active episode.