The Yashan pluton, outcropped in the west end of Pingxiang-Shaoxing suture zone which is referred as the eastern section of Qin-Hang metallogenic belt, is one of the most important rare-metal granitic plutons with Ta-Nb mineralization in South China. It is a composite pluton formed via multi-stage magmatic evolution, which can be roughly distinguished into protolithionite-muscovite granite, lepidolite granite and topaz-lepidolite granite from early to late. Zircon LA-ICP-MS U-Pb dating yields an age of about 150Ma, indicating it was generated in Late Jurassic. Geochemically, the Yashan granites are enriched in silica, depleted in magnesium and iron, thus are highly-fractionated with differentiation index (D. I) values mostly larger than 93. They also show subalkaline, and strongly peraluminous signatures with agpaitic index (AKI) values less than 0.80 and aluminum saturation index (A/NKC) values over 1.20. The granites are high in Cs, Rb, Th, U, Nb, Ta, low in Ba, Sr, REE, and exhibit distinct negative europium anomalies（δEu=0.04~0.25）. With increasing degrees of fractionation, the Na2O/K2O and Ta/Nb ratios, the fluorine contents, the europium depletions and the REE tetrad effect of the pluton increase, while the total REE abundances and the crystallization temperatures decrease. The Yashan granites have low εNd(t) values (=-10.4~-10.7) and CaO/Na2O ratios(<0.3), indicating that they were likely originated from partial melting of metamorphic pelitic rocks in crustal basement. However, the granites show highly variable zircon Hf isotopic compositions with εHf(t) values range from -14.8 to 0.7, implying that some mantle materials might have contributed to magma genesis. Based on a synthesis of petrology, geochronology, elemental and isotopic geochemistry, we suggest that the Yashan pluton should be ascribed to highly-fractionated S-type granites, and the Ta-Nb mineralization of the pluton was controlled jointly both by highly fractionation of the magma and by fluid-melt interaction during the late satge, while the former is likely the main mechanism for the enrichment of tantalum and niobium.