The Liajiagou deposit, a massive granite pegmatite-type lithium deposit, is located in the western part of Sichuan Province. Currently, the shortwave infrared spectroscopic properties of muscovite in the Liajiagou deposit remain unknown, and a deeper understanding of the correlation between its chemical composition and spectral characteristics is required. This study examines multiple generations and types of muscovite in the pegmatite of the Li Jiagou ore deposit. Microstructural observations, shortwave infrared (SWIR) spectroscopy, and electron probe microanalysis (EPMA) were performed. The muscovite in the pegmatite was classified into three generations: ①Primary muscovite (MS), formed during the magmatic stage, is characterized by high concentrations of aluminum (Al) and potassium (K). The absorption peak of muscovite at 2 200 nm (Pos2200) displays a limited variation range, ranging from 2 201 to 2 202.8 nm. The absorption depth at this peak (2200 Dep) often remains below 0.25. Additionally, the illite crystallinity index (IC value) typically falls within a narrow range of 1 to 1.5. ② During the magma-hydrothermal transition stage, transition muscovite (TM) becomes enriched in Li elements as a result of the exsolution of volatile-rich fluids. The Li₂O content in TM varies between 2.53% and 6.22%. Additionally, Pos2200 demonstrates a concentration peak centered at 2 200～2 201 nm. Most 2200 Dep values are below 0.5, whereas IC values remain consistently high, often exceeding 4. ③Hydrothermal muscovite (HM), predominantly formed via fluid metasomatism, exhibits the shortest Pos2200 values, with 2200 Dep readings mostly below 0.4 and IC values ranging from 2 to 4. The Al—OH absorption peak of muscovite in the Lijiagou pegmatite indicates variations in the elemental composition, including Si, Al, Fe, Li, and other constituents. During the transition from the muscovite (MS) stage to the topaz-muscovite (TM) stage, changes in elemental composition and substitution mechanisms primarily influence the shift in muscovite's characteristic absorption peak wavelength. In contrast, temperature becomes the primary determinant during the hydrothermal (HM) stage. Comprehensive research highlights the potential of the characteristic absorption wavelength (2 200～2 201 nm) of the muscovite Al—OH peak, coupled with an illite crystallinity value greater than 4, as effective indicators for mineral exploration in the Lijiagou pegmatite.