Abstract: The quantitative experiments for study of relationship between heavy oil composition and its viscosity are made. The result show sthat the relationship of exponential function occurs between percentage content of saturated hydrocarbon, aromatic hydrocarbon, neutral non-hydrocarbon, acidic non-hydrocarbon, colloid and bitumencarb in heavy oil and its viscosity. Among them, the viscosity of heavy oil decreases.with the increase of contents of saturated hydrocarbon and aromatic hydrocarbon, and increases with the increase of contents of neutral non-hydrocarbon, acidic non-hydrocarbon, colloid and bitumencarb in the form of exponential function. The degree of the influence on the viscosi-ty is as follows: colloid and bitumencarb>acidic non-hydrocarbon>neutral non-hydrocarbon, the former is the most important factor to affect the viscosity of heavy oil or absolutely contributes toit. This is coincident with the results from other experiments. Hence, to decrease the conten of neutral and acieic non-hydrocarbons collaid and bitu mencarb will effeetively decre ase the viscosity of heavy oil.

Key words: heavy oil, family composition, viscosity, ex ponential function