The Three-Gorges Dam on the Yangtze River is situated on the intact rock mass composed of diorite-granite at the southern termination of the Huangling block. The Huangling block as a sub-plate having double-layer structure (crystalline basement and sedimentary cover) in China continent keeps constant and slow uplifting as a whole since its formation in the Indosinian movement. Tectonic deformation within the block is not significant, with exception of a slight southeastward tilting. The block is confined by many active structures, of which the sub-longitudinal Yuan*an and Xiannushan deep fault zones are the main strongly seismogenic zones. The Yuan´an fault zone represents a regional boundary between West Henan, West Hubei and West Hunan mountainous regions as well as the Nanyang, Jianghan and Dongting Lake basins, with a total length of more than 1000 km. Two times M 6.5 earthquakes (the Changde and the Nanyang earthquakes) had occurred in the fault zone in historic time and the distance between the two epicenters is about 500 km. The Xiannushan fault one extends along the Xiangxi River northward and ends at the Qingfeng fault. It runs southward across Yuyangguan Pass and then its trace is unknown. Total length of the fault zone is more than 220 km. The fault zone has tectonic condition for occurrence of M 6 earthquake. The possible seismic risk for the dam may come from these two strong seismogenic zones, thus the seismic intensity influencing the dam was estimated to be 6°〜7° and the horizontal peak acceleration to be 0.1〜0.15 g.