The western Yunnan area is a natural laboratory with fully developed and best preserved Tethyan orogen in the world.Seismic tomography reveals a slab-like high velocity anomaly down to 250 km beneath the western Yunnan Tethyan orogen,to its west there is a low-velocity column about 300 km wide.In the region from Lancangjiang to Mojiang an obvious low velocity in the lower crust and uppermost mantle overlies on the slab.Synthesizing the available geological and geochemical results,the present paper demonstrates that this slab-like high velocity anomaly is a part of the subducted plate of Yangtze continental segment after the closure of Paleotethys.The collision of India and Eurasia continent starting from 50-60 MaBP might trigger thermal disturbance in the upper mantle and cause the uprising of asthenosphere,in that case the subducted Yangtze plate could be broken off,causing Cenozoic magmatic activities and underplating in the Lancangjiang-Mojiang region.