Abstract: Lithologic reservoirs have become the important targets of onshore oil exploration in China, and studies on their formation conditions and processes provide a guide for continental hydrocarbon exploration. Since the exploration of lighologic reservoirs in western Qaidam Basin is still in the starting stage, there are insufficient researches on hydrocarbon accumulation process. Aiming at Hongliuquan oil reservoirs in the south of western Qaidam Basin, fluid inclusion, crude-oil geochemical and quantitative fluorescent analyses were conducted in this study. On this basis, the evolutionary process of Hongliuquan oil reservoir was analyzed in terms of fluid evolution. The results show that the crude oil in the lower reservoir of Lower Ganchaigou Formation of Hongliuquan is originated from the parent source rocks of saline lacustrine basin, which is homologous low-maturity crude oil with consistent characteristics. However, there exists no high-maturity crude oil. In this region, three kinds of hydrocarbon inclusions were developed, i.e., low-maturity yellow fluorescent gas-liquid hydrocarbon inclusions in the early stage, blue fluorescent gas-liquid hydrocarbon inclusions and associated gas inclusions in the late stage. This oil reservoir underwent a formation process from low-maturity oil charging in the late sedimentary stage of Ganchaigou Formation (about 26 Ma) to the sedimentary stage of upper oil sand formation (5 Ma), till current adjustment and transformation of hydrocarbon accumulation. Blue fluorescent gas-liquid hydrocarbon inclusions and gas hydrocarbon inclusions are the products of low-maturity hydrocarbon in the early stage through fractionation and degasification in the process of adjusting and migrating upwards to shallow layer along the fault translocation system formed in the late tectonism.