Abstract: B values of five seismically active periods and four sei smically quiescent in China's continent arecalculated. The results show that theb value of the sei smically active period is obviously low er than that of the seismically quiescent period. The b value of the seismically activ e period is betw een 0.72 and 0.76, and tha tofthe seismically quiescent is in the range from 0.86 to 1.06. The mean ofbvalue of the seismically active and quiescent periods is 0.75 and 0.97 respectiv ely. Up to March 2000, theb value of the fif th seismically active period is 0.87, betw een the mean of bvalue of the seismically active period and that of seismically quiescent period, and is obviously higher than that of the sei smical ly active e period. Therefore, the fif th seismically active period beginning in 1988 in China's continent might not end yet, there could be some strong er earthquakes with M≥7.0 occurring in the future.

Key words: Seismically active period, Seismically quiescent period, b value, Seismicity tendency, The mainland of China