Abstract: Referring to the mature viscosity reduction process of heavy oil at home and abroad, a program of mixing Fengchen Heavy Oil with diesel to reduce viscosity for the pipeline is put forward according to the processing technology from Karamay Petrochemical Company. Features of Fengchen Heavy Oil, characteristics of the mixed oil, mixing process, hydraulic and thermal conditions under different throughout, minimum startup throughout, maximum throughout and safe shutdown time are studied in this paper. The results show that the mixed oil shows Newtonian fluid characteristics in a certain temperature range and the mixing process can meet the operation requirements under accident conditions and low throughout at initial production. Minimum mass fraction of diesel added which meets the designed throughout is 20% at low viscosity, minimum mass fraction of diesel added which meets designed throughout is 25% at high viscosity, and pipeline capacity spans a wide range at low viscosity and high viscosity. The smooth commissioning of Fengcheng super heavy oil export pipeline can provide a reference to the design of longer and larger throughout heavy oil pipelines in the future.