Abstract: To reduce the production cost of marine fuel oil, the light oil from mid-temperature coal tar (coal-light oil) was used as a low-cost blending component, and therefore the blending method was studied. The gradient viscosity method, which simulates the property changes of heavy marine fuel oil in the process of storage after rapid aging, was established. Four factors of gradient density difference, viscosity, acid number, total deposits after rapid aging were used as stability indices. Among of them, the viscosity difference was taken as the major indicator to determine the stability of the blending system. The results show that the highest proportion of coal-light oil which can mix with asphalt, diesel from coal tar and shale oil is no more than 17% to ensure the stability of fuel oil. It is found that the properties of the samples after rapid aging for 10 h at 120 ℃ are similar to that of samples aged for15 days at room temperature.