Leucogranitics rocks, crop out in the eastern Tethys Himalaya Cuonadong dome, southern Tibet, have characteristic minerals such as muscovite, garnet and tourmaline, and show the characteristics of highly differentiated magmatic rocks. From two-mica granite, tourmaline granite to garnet granite, alkaline feldspar is orthoclase, plagioclase evolved from oligoclase to albite, the content of Al₂O₃ and Na₂O in muscovite increased gradually, reflecting the evolution trend of granite towards aluminum-rich and sodium-rich. In the two-mica granite, the X_Fe and Al^Ⅵ of biotite increase gradually, which indicates that there is crystallization differentiation evolution in the two-mica granites. The variation of the contents of X_vac, Al, Mg and Fe in tourmaline reflects the increase of Na content in the magmatic crystallization environment from tourmaline granite to granite pegmatite, indicating that the degree of crystallization differentiation of granite pegmatite is higher than that of tourmaline granite. The characteristics of garnet with high X_Fe and X_Mn values are also the marks of highly fractionated granites. The Cuonadong two-mica granite was formed by long-term crystallization of a crystal mush composed of early magmatic crystalline minerals and residual parent magma, while tourmaline granite and garnet granite are formed by derivative melts separated from crystal mush.