Tarim basin is the craton block south to the Qinghai—Xizang(Qinghai—Tibet) plateau, which didn’t deformed intensively and kept stable and the geothermal state was also not changed abruptly during the collision between Indian Plate and Eurasian Plate. The geothermal lithosphere is about 250km thick, which is determined by the surface heat flow and the lithosphere thermal parameters when the thermal state is steady. Whereas the seismic thermal lithosphere is about 150km thick, which means the Tarim lithosphere is not steady and became thinner. In this paper, writers analyzed the Tarim lithosphere thinning mechanism based on the tectonic thermal evolution quantitative method, and discussed three possibilities:the hotter India asthenosphere intruded under the Tarim lithosphere and made the Tarim lithosphere became unsteady;the bottom of Tarim lithosphere is heated by friction of the atheonosphere flow and washed off by the hot asthenosphere; the Xizang (Tibet) lithosphere delamination induced the convection, and the upflowing mentle heated the bottom of the Tarim lithosphere and make it enthinning.