A series of leucogranites occur in lenticular and banded forms in the Altay high-grade metamorphic zone, Xinjiang. According to their mineral assemblages, these leucogranites can be divided into three groups: Al2SiO5_bearing leucogranites, muscovite-plagioclase leucogranites and muscovite monzo-leucogranites. An analysis of major elements shows that these leucogranites belong to S-type with A/CNK being 1.1～2.14. From the muscovite monzo-leucogranites through muscovite-plagioclase leucogranites to Al2SiO5_bearing leucogranites,SiO2 contents increase and Al203, Na2O and K2O contents decrease. The phase relations in pTpseudosection for the NKFMASH system and the calculation of melt composition at different pressures and temperatures show that the melts of Al2SiO5-bearing and muscovite-plagioclase leucogranites might have originated from an uplifting process of the kyanite-type metamorphic zone, with no relation to the muscovite dehydration-melting reaction. Moreover, the Al2SiO5-bearing ucogranites were probably not directly crystallized from the melt, but had to do with some losses of alkaline components through fluids. The uscoviteo-leucogranitesprobably originated from a heating process through the muscovite dehydration-melting reaction. The modeling of phase relations alsoindicates that the staurolite dehydration-melting reaction must have played a very important role in the melt formation.