In this paper,we determined earthquake sequence location in the Xingfengjiang area from June 2007 to July 2014 and 3D P-wave velocity structure by a simultaneous inversion method. On that basis,we studied the occurrence features of active tectonics and the earthquake source mechanism. The results show the reservoir fracture system has the tendency of increase with the gradual depth from southeast to northwest,consistent with the gravitational field research results. There are 4 high velocity zones(HVZ)under the depth of 7-12km crust between the Xinfengjiang Reservoir dam and Dongyuan Xichang district. The max velocity of the biggest HVZ which is under Xichang is 6.3km/s. Under the reservoir dam there is a strong tectonic deformation zone,as the center exit Renzishi fault F₂,Nanshan-Aotou faults F₄,Heyuan fault F₁ and Shijiao-Xingang-Baitian fault F₅. 7 earthquakes with M_L≥5.0(including M6.1 in March 1962)occurred at the high gradient zone of the HVZ Ⅲ and HVZ Ⅳ edge which is under the reservoir dam since 1960,relativity energy releasing more thoroughly. Moderate seismic activity occurred at the HVZ Ⅰ edge which is under Xichang since 2012,which is the dangerous zone of M5.0 earthquakes in the future.