Abstract: In this paper, the fracture propagation processes of the Daofu, Sichuan earthquake (Ms -6.8) which occurred on Jan. 23 of 1981 and the Wuqia, Xinjiang earthquake (Ms = 6.2) which occurred on Feb. 13 of 1983 as well as their relevant fore and after-shocks are analysed by using body wave data. Based on the view point that the earthquake fracture processes are relative to the propagation and stop mechanism of faults, so the mechanical models of a single fault and a series of faults are presented to simulate the propagation and stop processes of earthquake faults and to study the space distribution relations among events of the earthquake sequence themselves as well as among an earthquake and its surrounding earthquakes. Upon the basis of theoretical and practical analysis, a more reasonable method to determine the fra-cure length of an earthquake fault and to determine the location and lengths of the active segments and locked segments of a pre-existing fault is presented in this paper. With this method the mechanical characteristics of earthquake sources occurring at different portions of the faults can also be explained and determined. Its application is preliminarily to the tendency of earthquake occurrence of the Xianshuihe fault in this paper.