The Jiajika pegmatite- type lithium deposit located in the southeastern Songpan- Ganze terrane of the eastern Tibetan Plateau is the largest hard- rock lithium deposit in China, and its paragenetic mechanism is still controversial. To understand the critical magmatic- hydrothermal process that leads to Li concentration of potentially economic levels in the Jiajika pegmatite- type lithium deposit, the association between Li enrichment and granitic magma evolution is investigated using Li- B- Fe- Nd isotopes along the entire 3211- m- depth of the JSD- 1 scientific drill core. The data of Li isotope (δ7Li) and Nd isotope (εNd(t)), together with consistently low Nb/Ta, Zr/Hf of the pegmatites and two- mica granites, suggest that the Jiajika pegmatites are more likely from magmatic crystallization of the Majingzi two- mica granite pluton. The boron isotope (δ11B) of tourmalines in granite and pegmatite in JSD- 1 scientific drill core vary from 9. 5‰to 7. 1‰, in line with the range observed in 90% of worldwide granites and pegmatites related to melt- fluid fractionation in fluid exsolution. In comparison of the measured data of δ11B vs. Li to the modeled curves indicates that the differentiation process of granitic magma follows an equilibrium crystallization model better than a fractional crystallization model and the extreme differentiation of granitic magma alone could not reach the solubility- saturation for spodumene in the pegmatite- forming melt. The δ56Fe values of bulk rocks in JSD- 1 vary from 0. 12‰±0. 02‰ to 0. 38‰±0. 02‰, and the significant Fe isotope variation reflect the combined results of biotite fractionation, hydrothermal alteration (tourmalinization), and garnet accumulation during multistage magmatic- hydrothermal processes. The compiled evidence of Li- B- Fe- Nd isotopes proves that magma differentiation accompanied by fluid exsolution facilitates the enrichment of Li during granitic magmatic evolution. The formation of the domal structure of granitic sheets due to the decompressing effect of magma ascent favors massive fluid exsolution at the late- stage granitic magma, which contributes to the deposition of spodumene dominated ore body at the shallower depth.