In this paper, we firstly demonstrated that the M_S8.0 earthquake occurred on the Wudu-Songpan-Maowen-Wenchuan-Luding seismic zone, which is delineated by the regional gravity anomalies and seismic activity. The main ruptured region of the earthquake was located on a segment that lacked strong earthquakes during the active seismic period, i.e. seismic gap. The seismic gap is very remarkable before the M_S8.0 event and the main event occurred in the period of decreased seismicity outside the gap area. The rupture process extended towards NE direction and exceeded the seismic gap region. Seismicity in and out the gap show different active features, therefore the aftershock seismicity is divided into NE and WS segments by the author. Researches on source rupture process, moment tensor inversion of M≥4.0 aftershocks, stress field inversion, as well as the stress drops of aftershocks reveal that there exists significant difference between the two segments in slip distribution on the fault, focal mechanisms of aftershocks, stress drops, as well as direction of the tress field. According to those characteristics and study on the stress triggering, it is suggested that the seismicity on the NE segment may be triggered by the main rupture starting on WS segment.