Abstract: Coal / oil co-processing technology is an important way for the clean and efficient utilization of coal and inferior heavy oil by coupling coal chemical technology with inferior heavy oil processing technology. Viscosi-ty-temperature characteristics of coal-oil slurry are the key factors affecting the design and operation of large-scale pulping,transportation,pressurization and preheating. Taking Tahe heavy oil,coal tar heavy oil and low-rank coal as research objects,the effects of concentration of coal-oil slurry,solvent properties,swelling time and pore structure of pulverized coal on the viscosity of coal-oil slurry were analyzed by thermogravimetric analyzer,Fourier infrared analyzer,surface pore structure analyzer and high temperature viscometer. The variation law of viscous-temperature characteristics of coal-oil slurry during slurry preparation and preheating was studied. The results showed that the concentration and solvent properties of heavy oil were the main factors affecting the vis-cosity of coal-oil slurry. When the concentration was more than 35% ,the viscosity of coal-oil slurry increased significantly. Under the same conditions,the viscosity of Tahe heavy oil-coal slurry was higher than that of heavy coal-tar-coal slurry. With the increase of swelling time,the viscosity of heavy oil-coal slurry increased as a whole. After 12 hours of swelling,the viscosity of two kinds of heavy oil-coal slurry increased rapidly,and the viscosity of Tahe heavy oil-coal slurry increased faster. After swelling,a new pore structure was formed on the surface of pulverized coal particles,which resulted in a large number of macropores and some micropores,resulting in an increase in the viscosity of coal-oil slurry. Dehydrogenation and oxygen absorption condensation of heavy oil during the preparation of coal-oil slurry were also important factors affecting the viscosity of coal-oil slurry. In the preheating process,the viscosity decreased rapidly with the increase of temperature,and the higher the concentra-tion,the higher the viscosity. When the temperature exceeded 140 ℃ ,the viscosity decreased to a lower value. When the temperature exceeded 240 ℃ ,the viscous rebound phenomenon began to appear. Besides,the higher the concentration,the lower the temperature at which the viscosity of coal-oil slurry rebounded,and the larger the rebounded range.