The Lijiagou granite pegmatite-type lithium deposit is a super-large ore deposit in western Sichuan. Currently, the enrichment mechanism of lithium in the pegmatite of the Lijiagou deposit remains unclear. This paper focuses on multi-stage and multi-type muscovite and cassiterite in the pegmatite of the Lijiagou deposit, conducting microstructural observations, electron probe microanalysis (EPMA), LA-ICP-MS analysis, and cassiterite U-Pb dating. The study categorizes muscovite in pegmatites into three types: ① primary muscovite (Ms), a product of the magmatic stage, with a relatively low-Li content ranging from 2 089×10^-6 to 4 561×10^-6; ② transitional muscovite (TM), formed during the magmatic-hydrothermal transition stage where melt and fluid coexist, resulting from the exsolution of volatile-rich fluid leading to the enrichment of Li element, with a Li content ranging from 8 173×10^-6 to 25 307×10^-6; ③ hydrothermal muscovite (HM), formed by fluid metasomatism, where the Li element gradually decreases during this stage (with a minimum of 642.7×10^-6). The microregional compositional characteristics indicate that the K/Rb and Nb/Ta values gradually decrease from Ms to TM, indicating a higher degree of evolution of the Lijiagou deposit. Meanwhile, cassiterite in the pegmatite is classified into four types, from early to late, namely, relatively uniform structure (Cst-1) → inhomogeneous core-edge structure (Cst-2, Cst-3) → white patchy structure (Cst-4), with gradually increasing contents of elements such as Fe, Nb, and Ti. Combine with the Ta/(Nb+Ta) value, it is inferred that cassiterite exhibits characteristics of early Fe enrichment and late Nb enrichment during magmatic evolution. The significant increase of Ti content in white patchy cassiterite (Cst-4) reflects the metasomatic action of hydrothermal fluids. Furthermore, U-Pb dating of cassiterite within pegmatite containing spodumene reveals the depositional age of the Lijiagou deposit to be 196.18±4.39 Ma (n=18, MSWD=0.62). Based on existing research, it is determined that there are two stages of mineralization in the Lijiagou deposit, with ages of 211~205 Ma and 199~186 Ma, respectively. This paper believes that the mineralization process of the Lijiagou pegmatite experienced a melting-fluid evolution stage. The fluid exsolution resulted in the enrichment of Li element, which entered the spodumene lattice and precipitated into ore after reaching supersaturation, ultimately forming the Lijiagou pegmatite-type lithium deposit.