Abstract: A combined catalyst system with iso-dewaxing catalyst as a core and relative hydro-technologies were used for production of high viscosity and high viscosity index base oil. The paraffin-based fraction of the 4th side cut of vacuum tower of Karamay Petrochemical Company, PetroChina was used as a feedstock. The industrial results show that the base oil with viscosity >8 mm2/s(100 ℃) and VI > 110 can be obtained by the above combined technology.