Abstract: Based on Rb,Sr,Sm,Nd,Pb isotopic analysis from the Cenozoic alkaline, high-potassium calci-alkalic volcanic rocks of Hoh Xil area in Qinghai-Tibet plateau,the origin of the volcanic magma and volcanic genesis are discussed in this paper.The result indicates that the magma of the Cenozoic major volcanic rocks originated from the EMⅡ,the few acidic rocks of high-εSr and high-εNd resulted from the later crystallization differentiation of the magama and that the genesis of the alkalic volcanic rocks are related to initial rift of enter-plate.These studies provide the evidence of peculiar "crust-mantle mixed layer" in Qinghai-Tibet plateau.