The Jurassic shale oil in the Sichuan Basin has the characteristics of high viscosity and high content of heavy components. The reservoir surface is oil wetting, which makes it difficult for oil flow in the pore throats of the formation. At present, there is a lack of research on the characteristics and mechanisms of viscosity increase in shale oil in the Sichuan Basin, and there is no effective technical method to reduce oil viscosity. In this paper, oil components experiments are conducted on the oil sample obtained from several wells in central Sichuan Basin. It is clear that the high content of asphalt and wax is the direct reason for the high oil viscosity. Based on the macroscopic emulsification experiment and the microscopic characterization experiment of oil/water interface, it is known that asphalt and resin reduce oil/water interfacial tension, and they accumulate at the oil/water interface and form a high-viscosity emulsion, resulting in further increase in oil viscosity. The experimental results show that the viscosity of emulsified oil increases to a maximum of 12.7 times the initial viscosity. In addition, the saturates and resin form a viscoelastic interfacial film on the oil/water interface, making the high-viscosity emulsion more stable. Based on FT-IR and high-resolution 1H-NMR experiments, the microstructure of the four components of oil is revealed, and it is clarified that asphalt is more prone to form conjugated π bond association structures, which is the key intrinsic reason for the increase in oil viscosity. Asphalt and resin are the key components to reduce the oil/water interfacial tension. The higher the content of asphalt and resin, the lower the interfacial tension, which will promote the formation of crude oil emulsion.