Combining the variations of earthquake intervals and magnitudes. the activity features of mod-erate or stronger earthquakes in whole country and the main seismicity areas in China during this century are analyzed Most of intervals are within 5.5a, more than half are within 2.5a, and the maximum valve of interval is near 18a. After 1950s, activity weakened obviously for earthquakes of M ≥7.5 and M ≥7.0 all over China, M ≥7.0 in Qinghai-Xizang block (QXE), and after 1970s, it did so for shocks of M ≥7.0 in Taiwan, M ≥6.0 in North China, and M ≥6.0 in Sichuan. The influence of strong earthquakes which occurred in northern part of QXB from 1920s to 1930s on the seismicity of this region ended in 1970s, then, activity of 5.0 ≤ M ≤ 6.5 earth-quakes strengthened from 1980s clearly. The high tide of Yunnan seismicity formed after 1970s, in fact, was enhanced from 1960s. The typical process of strengthening before strong earthquakes is showed in North China and Taiwan, and that of attenuation after strong earthquakes is showed in Ganst-Ningxia-Qinghai (GNQ), The stress field of great triangle region, stress field of east part and the global scale stress field which are controlling the seismicity all over China have a stable pe-riod about 20a for a long time, while the later delayed about 1/4 period for the former in proper order, and the two former played a leading role. The seismicity along the eastern and northern edge of QXB include the important roll of QXB crust matter flowing toward east besides influence of stress field in east part. We should follow with interest the possibility of Sichuan M ≥6.0, GNQ M≥6.0 Gansu M ≥5.0 and Xinjiang M≥ 7.0 earthquakes in future years.