Amphibole and biotite are dark-colored minerals commonly found in highly differentiated alkaline granite containing REE-bearing and rare metal-bearing minerals. The different compatibilities of amphibole and biotite for different elements (especially rare metals and rare earth metals such as Nb, Ta, Zr and REE) make their characteristics of major and trace elements become the "log" of magma evolution, which has a significance in the reconstruction of the petrogenesis and mineralization process of ore-bearing magma. In order to determine the enrichment and distribution process of elements such as Nb and Ta during the magmatic crystallization, the authors studied mineral chemistry of amphibole and biotite in the Boziguo'er alkaline granite pluton in Baicheng, Xinjiang, by means of electron microprobe (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The amphibole in the pluton is arfvedsonite, which is generally characterized by high Na and Fe and relatively poor Ca (<0.15 apfu), Mg (<0.06 apfu) and Ti (<0.07 apfu). The uniformity of the composition and the deficit of LREE suggest that the amphibole was crystallized at the late stage and a large number of LREE-rich minerals were crystallized before amphibole. According to the association relationship, the biotite is divided into two types(type-A and type-B)in this paper, which have different chemical compositions. Compared with type-B, type-A has a higher content of F (3.81%~4.82% in type-A and 1.68%~3.65% in type-B) and SiO₂ (41.5%~43.3% in type-A and 35.9%~38.5% in type-B), and a lower content of TFeO (28.0%~31.4% in type-A and 32.2%~35.7% in type-B) and Al₂O₃ (6.45%~7.62% in type-A and 9.70%~11.00% in type-B). The different values of fluorine in biotite and amphibole indicate the enrichment and saturation process of fluorine in the crystallization process and a large number of REE-bearing and rare metal-bearing minerals crystallized on account of fluorine saturation. Due to the incompatibility in the main minerals, the ore-forming elements Nb and Ta should be gradually enriched in the melt, whereas the Nb/Ta ratios of the main minerals and most of the secondary minerals are higher than those of the bulk-rock, resulting in "Ta-missing". Combined with previous studies, it is believed that the combination of the volatile saturation and the crystallization of zircon caused the separation of Ta from the melt.