By using gravity and seismic investigation data collected from the Qinghai—Xizang(Tibetan) Plateau, we obtain 3D crustal density disturbance and seismic tomography images. The density imaging results show that the Cenozoic rifts located in Xizang extend to bottom of the middle crust，about 42km. Low density and seismic velocity anomalies also occur in the lower crust, indicating the lower crust creeping flow. Different from other well- known continental rift zones such as the East Africa and Baykal, The Xizang Cenozoic rifts contains several parallel rifts that have special origins related to the continental- to- continental subduction, can be called the continental subduction type of the rifts. The subduction makes both crustal orthogonal compressional and extensional zones, and some deformation gaps, which become the original concentration space of underground stress to develop the rift. The formation process of the rift system contains the following steps. (1) The continental subduction causes crustal faulting and earthquakes; (2) stress concentration around the deformation gaps; (3) the compressional stress diverges ahead along the subduction direction and turns to orthogonal extensional zones, resulting in crustal faulting and earthquakes along the rifts; and (4) crustal rebound and deformation after every earthquake event, expanding the rifts. The lower- crust flows also have some effect on the rifting, as the creep deformation of the flow may make diapiric intrusion upward. The diaper process produces extensional stress to middle and upper crust, contributing to the growth of the continental subduction type of rifts. In addition, subside of remaining plate of the Tethys Ocean in Tibet asthenosphere has induced upwelling of hot mass in deep, resulting in mass creeps in the crust and formation of the rift system.