Abstract: Abstract：Based on 1：250000 regional geological survey in a blank area of northern Tibetan Plateau, the authors studied the middle Kunlun fault belt in such aspects as structure properties and rock types, geochemistry and sources of the basement metamorphic rocks (including the meta-basic volcanic rocks and metapelite), cover sedimentary rocks, Precambrian felsic intrusive rocks, and mafic-ultramafic intrusive rocks. The results show that the north and south sides of the Kunlun fault zone is completely different in continental lithosphere, sedimentary rocks, crust and mantle structure, physical properties and geochemical composition. It is thus suggested that the East Kunlun orogenic belt is actually a land mass of the collision between two continental-margin orogenic complexes. Therefore, the north land mass and the south land mass did not belong to the same land mass in Proterozoic, and the middle Kunlun fault was exactly the boundary between Eurasia and Gondwana land.