Detailed petrographic observation and systematic mineralogical chemistry studies of the Xinzhai granite from the north Guangxi were performed in this paper. Based on electron microprobe analysis (EMPA) data, the authors calculated pressure, temperature, oxygen fugacities (log f_O2) and H₂O in co-existent melts conditions of the crystallization of these granites. According to the petrographic features, there are three types of amphiboles in Xinzhai amphibole granite, i.e., euhedral amphibole, unaltered subhedral/anhedral amphiboles and strongly metasomatized subhedral/anhedral amphiboles, which are products of crystallization or metasomatic alteration of the Xinzhai intrusion formed at different depths and stages in the process of emplacement. The EMPA results show that the major element compositions of amphibole in Xinzhai granites are varied depending on crystal morphology, characterized by the decreasing of Al₂O₃, FeO^T, Na₂O, TiO₂, K₂O but increasing of MgO and SiO₂ during magmatic emplacement. The values of crystallization pressures estimated from aluminium-in-amphibole barometry of the euhedral amphibole and unaltered subhedral/anhedral amphiboles are 0.28~0.30 and 0.19~0.26 GPa respectively, indicating that the emplacement depth of the Xinzhai pluton should be greater than 11.3 km. Furthermore, the corresponding crystallization temperatures of emplacement calculated with the amphibole-plagioclase thermometry and amphibole thermometry of the euhedral amphibole and unaltered subhedral/anhedral amphiboles are 767~783℃ and 740~764℃ respectively. Based on the p-T conditions of the pluton crystallization, it is suggested that the Xinzhai pluton experienced isothermal decompression and polybaric crystallization during the emplacement. The calculated oxygen fugacities of the unaltered amphiboles are in the range of ΔNNO+0.1 (log f_O2=-13.5)～ΔNNO+0.5 (log f_O2=－12.9), indicating a relatively high oxygen fugacity. Moreover, the fractional crystallization enriched the water content of the residual melt (4.9%~6.4%) and experienced exolved aqueous fluids when the evolved magma intruded into the shallower depth (7.0~9.5 km) mainly due to depressurization. Genetic mineralogy studies show that amphibole in the Xinzhai granite belongs to calc-alkaline intermediate and acid magma, which was likely derived from a crust-mantle mixed origin and continuously contaminated by crust materials in the process of emplacement.