The types of sequences and features of foreshock and aftershock activities of 18 M_S≥5.0 earthquakes since 1970 along Qilian-Haiyuan seismic zone are studied.The space distribution of types of the sequences along the zone is analyzed.The results show that 44 percent of events are mainshock type,and 55 percent of events are isolated type. The sequences in Xiji-Haiyuan-Guyuan segment of the zone are isolated type, that in the middle eastern segment of the zone are mainshock type, that in the middle segment of the zone are isolated type and mainshock type both, and that in the western segment of the zone are isolated type. The result of the seismicity trend judging after the Jingtai M_S5.9 earthquake on June 6, 2000 by using study results of this paper consists with real facts.