The effect of temperature, harmonic ration, surfactant and shearing to fuel oil prepared by blending heavy oil and coal tar were detailedly studied. The results show that the viscosity of the blended oil increases gradually with the increase of harmonic ration from 2:1 to 7:1. It shows that the viscosity decrease rate can be divided into two sections with temperature increasing: In the first section, increasing the temperature of reaction, the viscosity of blended oil decreased sharply, and the decrease rate reached about 160 mPa.s / degrees C. In the second section, the viscosity of blended oil changed slightly, the average decrease rate about 24 mPa.s / degrees C. It was caused by the change of intermolecular interaction energy and van der waals force. The further research shows that, adding nonionic surfactant or shearing decrease significantly bled oil viscosity. At 50 degrees C, adding 3 parts per thousand nonionic surfactant, bled oil viscosity decreased 900 mPa.s, and bled oil viscosity decreased 1200 mPa.s by shear. Compared without using shear, the viscosity of the blend oil was decreased by 27% at 50 degrees C. The mathematical model between viscosity and temperature has been derived by using mathematical method. In the first section (<70 degrees C), the mathematical model between viscosity and temperature can be described as lg v(m)=Sigma x(1) lg v(1)-K-1 - 11.3 T + 0.01 T-2. In the second section (>70 degrees C), the mathematical model between viscosity and temperature can be described as lgv(m)=Sigma x(1) lgv(1) - K-2 - 1.1 / {1 + exp [(T - 351.5) / 6.3 ]}.
