Rare metal minerals are important for the development of modern industry and science and technology. The origin and mineralization of pegmatite deposits, which serve as the main sources of rare metal minerals, need to be studied thoroughly. The common disputes include the crystallization differentiation of granites, partial melting of the crust, and magma liquid immiscibility. Studies have shown that lithium isotopes underwent negligible fractionation during crustal anatexis and therefore provide strong evidence for the magmatic source of granites and pegmatites. Mainly from the three aspects of the origin of granite pegmatite, lithium isotope fractionation mechanism, and lithium isotope application in pegmatite deposit, this paper systematically summarizes some research progress made in recent years both in China and abroad. Domestic and foreign geologists have elaborated the Li isotopic composition of the granite pegmatite according to the lithium isotope fractionation mechanism. It is believed that the genesis of the pegmatite deposit may be mainly the crystallization of granite or the partial melting of the crust. However, the study of the origin of in pegmatite deposits is not mature enough and hence more work needs to be done.