Through studying eighteen trenches along the Haiyuan fault, ten paleoearthquakes were determined since ten thousand years ago. They have different rupture scales. The first and last events ruptured along the entire fault; the other events ruptured along secondary segments. The paleoevents are characterized by clustering in time and migrated back and forth from the west segment to middle - east segment. The magnitude of earthquakes along the entire ruptured fault is about 8. 5 and of those along the secondary ruptured segments is about 7.5.