Niujiaogou uranium occurrence is one important Na- metasomatic uranium occurrence in Longshou Mountain, Gansu Province. The potassium- sodium mixed metasomatic rock, recently discovered at the periphery of the occurrence, is pretty rare t in this area. In order to investigate the potassium- sodium mixed metasomatism in details, this study carried out petrology, mineralogy, geochemistry, and isotope chronology analyses for the Niujiaogou medium- coarse grained granite and altered rocks. Geochemical study shows that the Niujiaogou medium- coarse grained granite is high- K calc- alkaline granite formed in the post- collision setting of QilianLongshou orogeny in early Paleozoic (445.2±7.8Ma), from which the granite formed characterized by medium Si, rich alkali and weak peraluminous, low Fe and Ca, and poor Ti, Mg and P. Potassiumsodium mixed metasomatism gives rise to the formation of porous altered granite→ snowflake calcilization granite→ claretcolored granite with poor quartz and no dark minerals→ pseudo- chloritization granite and finally to primary granite successively from inner to outer. The potassiumsodium mixed hydrothermal fluid extracted iO2, TiO2, FeO, Fe2O3, MnO, MgO, CaO, P2O5, REE, Ba, Sr, Zr, Sc, Cr, Sr, Co, Mo, Hf, Bi, Sb and Pb from granite. Some components such as Na2O, K2O, MnO, Th, U, Rb, Nb, Ta, W and Sr precipitated in porous altered granite. CaO, MnO, Na2O, Th, U, Nb, Ta, Rb and HREE migrate with calcite into snowflake calcitization potassiumsodium mixed alteration zone, while TiO2, FeO, Fe2O3, MgO, CaO, P2O5, V, U, Se and Zr are enriched in claret- colored potassium- sodium mixed metasomatic zone. The potassiumsodium mixed metasomatic medium- coarse grained granite is characterized by brittleness, fragility and porosity, which provide favorable basis for Na- metasomatic uranium mineralization. Their emplacement age further confirms that Na- metasomatic uranium mineralization started around 444Ma～442Ma.