Abstract: Experiments carried out on the system granite-H2O-HF at 0.1G Pa show that the upper temperature limite raises for thestability field of quartz and falls for the stability fieldof alkali-feldspar as F contents increase. The calculated results of quartz, alkali-feldspar crystal-liquid equilibriumshow that the activity of SiO2 in melt increases and the activities of NaAlSi3O8 (Ab)and KAlSi3O8 (Or) decrease, with a greater decreasing extent for αAbL than αOrL. These systematic changes are believed to be caused by F complexing with A1, Na, K, but not Si in melt, and are consistent with F decomposing AlO2- tetrahedra and preferentially forming coplexes with Al, Na rather than K. The comparison between effects of F with that of H2O on phase equilibrium suggests that the maximum differenceaffectingmelt structure between F and OH is F complexing without Si and OH complexing with Si in granitic melt.