Objectives: In order to perform 3D seismic body- wave tomography, one needs seismic data observed on the Qinghai—Tibet Plateau. there are 412 local seismic stations that have digitized data after 2008, providing possibility for the seismic tomography. This paper presents results of 3D P- wave tomographic images of the asthenosphere under the Qinghai—Xizang Plateau for studying continental dynamics. Methods: After combining and processing the local seismic data, We select more than 260000 rays and their travel- time for the 3D seismic inversions, obtaining 3D velocity images of scale of 1°×1°×20km. Results: Our 3D P- wave tomography results show that patterns of the velocity disturbance change greatly with depth, indicating the upper mantle velocity perturbation and structure characteristics. Different from craton areas, the asthenosphere under the Qinghai—Xizang Plateau contain many local anomalies of both high and low velocities, reflecting magnificent energy and mass motion during collision between the Eurasia—India plates. A very clear high- velocity anomaly lies on the 410km discontinuity on the asthenosphere between 28°~40°N，indicating the today's position of the Tethys Ocean Plate. Based on the north- wade movement velocity of the India plate during 60~10Ma, we can look back upon past position of the Tethys Ocean Plate, therefore reconstructing the plate movement pattern around the Qinghai—Xizang Plateau. The results show that the Tethys Ocean Plate reached the asthenosphere under the Qinghai—Xizang Plateau about 50Ma, and then slowly sink to bottom of the asthenosphere, causing upwelling of the asthenosphere and big- scale volcanism in the north part of the plateau. Conclusions: The results indicate that not all of ocean plates subducted into the bottom of the upper mantle, some of them might subducted into the bottom of the asthenosphere and stayed there for many million years.