Abstract: the seismic activity is very active in Qinghai-Tibet plateau, which is the joint area of Eurasian plate and Indian plate, and many strong earthquakes have occurred there in recent years.On Nov.14, 2001, an M8.1 earthquake occurred on the west pass of Kunlunshan Mountain, which is the largest one in recent 50 years.The earthquake generated a 300km surface fracture with a 5~6m horizontal shift.In order to study its geometrical parameters and mechanical features, Center of Exploration Geophysics, CSB set up a seismic array along the zone from late March to middle April, and more than 800 aftershocks were recorded.Through the observation we obtained clear seismic phases of the fault, and mastered its characteristics.