Abstract: In order to comprehensively study the genetic relationship between Aral Rock Mass and the Pegmatite Vein group in Koktokay area, this work systematically analyzed the Zircon U–Pb isotopic age, geochemistry and Hf isotopic characteristics of the Be bearing pegmatite vein in the Ahersan area of the western Aral Rock Mass. The results show that the Zircon ²⁰⁶Pb^/238U weighted average age of the pegmatite vein is (203.9 ± 2.2) Ma. Its geochemical characteristics are high silicon, low titanium, rich aluminum, rich alkali, rich in large ion lithophile elements Rb, Th, U and rare earth elements La, Ce, Nd, Sm, and depleted in Ba, Nb, Ta, Zr, Hf, Sr, P, Ti. It belongs to typical low Ba, Sr rocks. The zircon isotope ¹⁷⁶Hf/¹⁷⁷Hf values range from 0.282714 to 0.282749, The range of ε_Hf(t) value is +2.56～+3.65, the age of t_DM^C model is 852～912 Ma. the similarity of Zircon U–Pb isotopic age, the correlation of geochemical characteristics, the similarity of ¹⁷⁶Hf/¹⁷⁷Hf and ε_Hf(t) values, indicates that they have a close genetic relationship. Based on the regional data, it is believed that the magmatic activities represented by the Mesozoic rare metal mineralized pegmatite vein and Aral Rock Mass are may originate from the partial melting of crustal materials such as Precambrian metasandstone and metamorphic mudstone, and significant crystallization differentiation occurred.