Objectives:3D seismic tomography has been carried out for imaging the mantle under the Qinghai—Xizang (Tibetan) Plateau, but has not been performed for imaging the crust beneath the Qinghai—Xizang Plateau. This paper presents results of 3D Pwave tomography of the Qinghai—Xizang Plateau for studying continental dynamics. Methods: We perform Pwave seismic tomography using seismic data collected from both the national and local stations for studying the crust beneath the Qinghai—Xizang(Tibet) Plateau, and obtain 3D crustal velocity disturbance images of scale of 1°×1°×20 km. We use more than 260000 traveltime picks for the inversion of Pwave velocity, producing accurate velocity images of the upper, middle and lower crust. Results: Our 3D P- wave tomography results show that patterns of the velocity disturbance change greatly with depth, indicating that the crust occurred interlayers detachment and near horizontal shearing, and therefore, the crustal movement cannot be described by the socalled “blockmoving”. The upper- crust and uppermost mantle of the Qinghai—Xizang Plateau are occupied by large areas of high velocity, indicating that rather solid upper- crust and uppermost mantle have already formed by frequent magmatic intrusions and crystallization after the subduction and collision processes. Therefore, the Plateau maintains as a whole. The volcanic zones located along Cocoxili and northern Qiangtang show low P- wave velocity anomalies from upper to lower crust, indicating that the collision caused rerupture of the East- Kunlun suture and a great amount of mantle magma uplift caused by volcanic eruptions, making contribution to the formation of the thick crust of the plateau. Our tomographic images also improve the conclusion drawn from crustal density imaging, and show that the Cenozoic rifts located in the southern plateau extend to bottom of the middle crust. Conclusions: Our results of the crustal Pwave seismic tomography support the following new discoveries: the lowercrust flows, the contribution of northernvolcanic zones and the southern rifting process.