Since early Cenozoic, the collision and ongoing continuous convergence of the Indian and Eurasian plates have resulted in the high elevation and thick crust of the Tibetan Plateau. Yumushan thrust belt is located at the north front of the Qilian Mountain, and is the newest joined part of the Tibetan Plateau. Its geometry and kinematics of the crustal deformation recorded the complex relationship between the tectonics, erosion and climate change of the newest evolution of the earth. The deep structure and uplift mechanism have been controversial for a long time. In this paper, the authors unraveled the crustal structure of the Yumushan thrust belt by the newest acquired deep seismic reflection profile. The Moho depth beneath the Yumushan belt is 45-48 km with a shallower trend to the north; the deep reflection structure and subsurface tomography velocity structure show the apparent transparent zone and high velocity zone beneath the Yumushan, which may represent the intrusion of a large amount of granitoids beneath the Yumushan related to the closure of the Qilian Ocean in early Paleozoic, and the uplift was driven by two back-back thrust faults. Combined with other geological and geophysical data, the authors propose a new growth pattern in the northmost Tibetan Plateau, which may shed some light on the northward growth as well as the basin-range coupling relation.