Abstract: This paper describes a viscosity reducing method for Orinoco Heavy Crude (Venezuela) with associating, dissolving and diluting techniques, applying the method, the viscosity of the heavy crude is descended below 500 mPa·s at 30℃ from 20000 mPa·s at 50℃, and the volume of diluents (naphtha, gasoline etc.) used is reduced to 18.6% from 25%. The viscosity versus concentration relationships reflecting the viscosity of the heavy crude and diluent's concentration are obtained to establish the relationship of mixture's viscosity, concentration and temperature through experiment. The author believes that the combined viscosity reducing technique provides a more effective method than an individual method, which is of general significance in viscosity reduction of heavy crude.