Abstract: Using wavelet method, we study the periodicity and its significance level(confidence) of seismic activity selected from two tpyes of regions (the China continent and adjacent regions and the China continent), based on different starting magnitude of strain energy(Benioff strain) and during different time segment. The results show that: ① For seismic activity in the Chinese continent and adjacent regions, the confidence of 23 years′ period exceeds 95%, and those of 45 years period and 90 years period reach up to 90%; ② There is an obvious period of 25 years in China continent, the confidence of which exceeds 95%; ③ The confidence of the same period would decline with the decrease of starting magnitude for both types of regions. The periodicity of 23 to 25 years, the confidence of which exceeds 95% in both China continent and adjacent regions and China continent has a realistic guiding significance to the prediction of seismic activity and quiescence. The periodicity of decades and century also shouldn't be neglected in the analysis of earthquake tendency.

Key words: Periodicity of seismic activity, China continent and adjacent region, China continent, Wavelet analysis