Aftershock distribution, focal mechanism interpretation, inversion result of source rupture process of the 2015 Ms8.1 Nepal great earthquake and Cenozoic tectonic of the Himalayan orogenic belt shows that the Ms8.1 great earthquake resulted from low angle subduction of Indian plate towards the Eurasian plate along the Main Himalayan Thrust (MHT) fault zone. The focal rupture propagated from northwest to southeast along the MHT trend, with an accumulated length of about 170 km and a maximum dip slip displacement of about 5 7 m. The focal rupture was active at most during the Holocene, with high frequencies and high magnitudes. Along the MHT, earthquakes with Ms ≥7.5 occurred very 500 years and the average interval of earthquake segmentation rupture was only 10 years or so during active phase of earthquakes. Historical records show that seismic activities migrated distinctly from west to east along the MHT during last 1800 years, revealing that four seismic gaps, including the Hindukush, western Nepal., Sikkim Bhutan and India Myanmar border area from west to east respectively along the MHT, occur in the Himalayan thrust belt, especially the last two gaps to the east of the 2015 Nepal earthquake vulnerable to geohazards. Collision between Indian plate and Eurasian plate is not only the driving force for deformation of present Chinese continent but the leading tectonic factor for frequent occurrence of strong earthquakes in China. Our study shows there is spatial temporal relation of big seismic activities in Himalayas, Qinghai Tibet plateau and adjacent areas, which are reflected by alternative occurrences of big earthquakes during active stages and vertical migration of big earthquakes perpendicular to the Himalayan orogenic belt. The previous seismic records in the Qinghai Tibet plateau and adjacent areas and analysis results of future seismic geohazards reveal that during a next new round of seismic activity in the Himalayan seismic belt, Chinese mainland will likely face the sever situation of seismic hazard, especially the regional active tectonic belt or faulting belt of the Qinghai Tibet plateau and adjacent areas at the late Quaternary will have a high risk for strong earthquakes. The areas includes: nearly N S trending rift zone and northwest right lateral strike slip fault zone in southern Tibet, Anning river Xiaojiang fault zone, Daliangshan fault zone, Natinghe fault zone, Wanding fault zone, Lancang Jinghong fault zone and Dali Lijiang graben belt of northwest Yunnan in Sichuan Yunnan block, West Kunlun thrust fold belt, Altyn Tagh fault zone, and main thrust fold structure belts around Tianshan mountain in the northwestern region of China etc. But less investigation for and study of active tectonics in southwest China has not only restricted much precise geological assessment for geohazards triggered by strong regional earthquakes but been the bottleneck for evaluation of crust stability to national planning and construction for urbanization and key engineering projects.