Renli super- large Nb- Ta deposit is located in the Jiangnan uplift orogenic belt at the intersection of Yangtze block and Cathaysian block and the southwestern margin of Mufushan rock mass, and it is a super- large and high- grade granitic pegmatite- type Nb- Ta deposit newly discovered in eastern China in recent years. In order to ascertain the geochemical characteristics of pegmatite in ore bodies and further summarize the metallogenic characteristics of rare metals in the area, and provide experience for prospecting and research of rare metals in Mufushan area and even in South China. In this paper, 13 ore samples from No. 5-2 ore body of No. 5 main vein borehole ZK1616 were selected for major, trace and rare earth element tests. The test results are as follows: SiO2: 70.2%~90.1%, Al2O3: 5.23%~16.4%, Na2O+K2O: 3.49%~11.5%, A/CNK: 1.42~3.28, total amount of dilute alkali: 202.0×10-6~1155.9×10-6, rare earth element content is very low, part of which exceeds the lower limit of measurement accuracy. A/CNK is obviously higher than granite A/CNK index and has higher differentiation index. Studies have shown that the pegmatites in the orebodies and their surrounding rocks (granite) are highly differentiated, silicon- rich, peraluminous, calc- alkaline granitic rocks. The study shows that the pegmatite and its surrounding rock (granite) in the orebody belong to highly differentiated, silica- rich, peraluminous and calc- alkaline granitic rocks, suggesting that the enrichment degree of rare metal elements is well consist with the differentiation and evolution degree of granite. The mineralization of rare metals is controlled by magma differentiation and evolution. In the late stage of differentiation, gaseous and hydrothermal fluids rich in F, H2O and CO2 release and migrate rare metal elements from surrounding rocks. Pegmatites with complex zoning formed through multistage is more favorable for the mineralization of rare metals.