Abstract: In this paper, the fast marching method （FMM） is used to calculate the theoretical travel time of the teleseismic P wave in our model. We inverted the relative travel-time residuals to obtain the relative velocity distribution of crust and upper mantle in western Tibet by subspace iterative algorithm. The results show that the high-velocity anomalies exhibit in the depth of lower crust of western Tibet, while in the depth of upper mantle, the range of the high-velocity anomaly gradually decreases from west to east. And there is an alternating distribution of high- and low-velocity anomalies in the east of our study area. Therefore it is considered that the Indian Plate subducted nearly horizontally within the Tibetan Plateau, and the subduction range in the west is larger. During the subduction process, the Indian Plate is being torn. Subsequently, the torn Indian Plate sank into the upper mantle, and the tearing gap affected the formation of Cenozoic rifts in western Tibet due to stress release.