Abstract: With methods such as polarizing and fluorescence microscope observation, homogeneous temperature and ice point temperature measurement and analysis of composition, a systematic study was conducted to acquire petrographic, salinity and homogenization temperature of fluid inclusions in the Yanchang Formation of the Triassic reservoir in the Ordos Basin. Combined with the thermal evolution of basin, fluid injection history and corresponding paleo-fluid potential were constituted. The oil and gas accumulations of reservoirs in the Chang2 and Chang6 sections were characterized by one stage, and might happen in the Middle Cretaceous, about 120-100 Ma.