The Jiajika pegmatite type lithium deposit in Kangdi of Sichuan Province is the largest lithium deposit in China. Nevertheless, researches are very insufficient on the source of its ore-forming fluid. More than 400 primary inclusions in the Jiajika deposit were analyzed by the authors. The results show that the homogenization temperatures of CO2-NaCl-H2O inclusions and brine inclusions change gradually into each other. When the homogenization temperatures are lower than 300℃,the salinity of CO2-NaCl-H2O fluid is lower than that of NaCl-H2O fluid. The capturing pressure of CO2-NaCl-H2O fluid is larger than that of NaCl-H2O fluid. These data show that the ore-forming fluid evolved from CO2-NaCl-H2O to NaCl-H2O with the falling temperature and pressure, which is similar to the fluid evolution of the Keketuohai pegmatite deposit in Altay and the Tanco deposit in Canada. The laser Raman test shows that the main compositions of CO2-NaCl-H2O fluid inclusions are CO2 and H2O，with no hydrocarbon detected, which is consistent with characteristics of the fluid derived from the mantle and related to magmatism. The composition of O and H isotopes is located in the area of magma water in diagram, and the δ13CV-PDB‰ values are -3.4‰～-7.3‰. The formation time of pegmatite dikes is later than that of the granite body. These characteristics indicate that the ore-forming fluid resulted from fractional crystallization of magma, with the participation of some connate water at the late stage.