Abstract: In order to prevent settling and excessive resistance in the process of coal-oil slurry conveying,the characteristics and mechanism of viscosity of coal-oil slurry in FCC slurry,coal tar heavy oil and low rank coal co-processing were investigated by using Rotary viscosimeter and high temperature viscosity meter.The results show that temperature has a great influence on the viscosity of coal-oil slurry under normal pressure and low temperature.The viscosity of coal-oil slurry decreases rapidly at first,and then slows down with the increase of temperature.The activation energy of coal-oil slurry during FCC slurry is higher than that of coal tar heavy oil. Under the condition of high temperature and pressure,the viscosity of coal-oil slurry prepared by decreases with the increase of temperature,and increases slightly between 350 ℃ and 370 ℃.The viscosity of coal-oil slurry prepared by coal tar heavy oil initially decreases with the increase of temperature.When the temperature exceeds 140 ℃,the viscosity of coal-oil slurry begins to rise.Then the viscosity reaches the maximum value at the temperature of 338 ℃,and then decreases with the temperature further increases.