Based on electron probe analyses of the minerals and bulk composition of the Ceno-zoic volcanic rocks from Yumen and Hoh Xil lithodistricts, Qinghai2Xizang plateau, the form-ing conditions including the temperature and pressure of those rocks are studied in this paper. According to the thermodynamic calculation results of mineral2melt equilibrium, the depth of the asthenosphere superface (about 75-130km) for the northern part of the Qinghai-Xizang plateau during the Cenozoic is suggested. Finally, this paper indicates that the Cenozoic vol-canic rocks in the northern part of the Qinghai-Xizang plateau mainly consist of shoshonite se-ries. Their forming temperature is 630-1039 ℃ and forming pressure is between 2.3-4.0GPa. The rocks were formed in the intracontinental orogenic belt, of which the primary mag-ma was originated from a particular enrichment upper mantle and accreted crust-mantle belt or directly from asthenospheric superface as a result of partial melting of pyrolite.