Abstract: Pre-hydrofined light dewaxed oil (200SN) and heavy furfural refined oil (650SN) from Daqing Refining and Chemical company were used as feedstocks to investigate the effect of new isohydrodewaxing catalyst PIC-812 with improved B acid and operation conditions of pre-hydrofining and hydroisomerization on viscosity index of base oils. The industrial data indicate that the improvement of B acid and the higher reaction temperature of pre-hydrofining and hydroisodewaxing can all increase the ring opening selectivity, resulting in higher viscosity index of base oil. Compared with the previous generation hydroisodewaxing catalyst PIC-802, PIC-812 shows a higher activity. The reaction temperatures of PIC-812 are 2 ℃ and 26 ℃ lower than PIC-802, respectively, with other reaction conditions being the same using PIC-802. Both the base oil yields increase by 4 % and the viscosity index can increase 4 to 9 points.