From Northeast to Southwest of Mufushan area in northeast Hunan province, the rare metal mineralization assemblages change from single to complex, and the metallogenic scale increases gradually, showing obvious spatial regularity. The Renli- Chuanziyuan rare metal deposit has the highest magmatic differentiation and evolution degree, and the most complex mineralization assemblages of the Mufushan area. In this paper, we carried out a detailed investigation on the mineralogical, geochemical and mica Ar- Ar chronological studies of the typical pegmatite, with the aim of revealing the geochemical characteristics of Be- Nb- Ta- Li- Cs pegmatite, discussing its genetic relationship with granite wall rocks and defining the metallogenic age of rare metals in the deposit. The No. 5 pegmatite of Renli- Chuanziyuan deposit is geochemically characterized by relatively rich in alkali with Na2O+K2O (5. 11~14. 02 %) and peraluminous (A/CNK=1. 04~2. 26). The pegmatite is distinctively enriched in Ta, Nb, Hf and Zr, relatively depleted in Ba and Sr. Strong enrichment of incompatible elements Rb, Cs, Nb, Ta, Zr and Hf indicates that the pegmatite magma has undergone sufficient differentiation and evolution. Mineralogical and geochemical characteristics show that the differentiation- evolution degree of No. 5 pegmatite of Renli- Chuanziyuan deposit increases gradually from border to core. But the representational geochemical indexes of pegmatite show obvious catastrophic relationship with the granitic wall rock. Based on the field contact relationship and chronology evidence, we inferred that the wall rock of two- mica granite is not the parent rock of rare metal pegmatites. The rare metal mineralization of Renli- Chuanziyuan deposit shows the characteristics of magma- hydrothermal two- stage mineralization. The Ar- Ar plateau age of lepidolite in the No. 5 pegmatite is 125. 0±1. 4 Ma, which represents the age of rare metal accumulation and mineralization in the near hydrothermal system at the late stage of magma differentiation and evolution.