Abstract: This paper is concerned with the process of concentration and diffusion of the regional seismicity before and after eight great earthquakes (M_s=7.0),Xingtai,Bohai sea,Tonghai,Luhuo,Yongshan,Haicheng,Longling and Tangshan,which took place in China during 1966—1976. The process might be divided into three stages: (1) seismicity was distributed mainly in the far-source area; (2) then it migrated and concentrated in the focal region and near-source area; (3) after the occurrence of great earthquake,seismicity diffused toward the far-source area gradually Finally,Rice and Rudni-cki's inclusion model of earthquake precursor and the idea of stress adjustment are used to understand the above process.