A pd-containing carrier-type cross-linking clay is used as catalyst and an industrial hydrocracked tail oil whose boiling point is over 350 deg.c as raw material. Through catalytic hydrocracking, a base oil of lubricating oil having super-high viscosity index, as well as excellent intermediate fraction as by-product are obtained. The reactive conditions are gentle, such as temp: 200-450 deg.C; pressure: 6-16MPa; liquid volume air-speed: 0.5-10/hour; and hydrogen-oil volume ratio: 500-2000. After fractional distillation of reactive resultant and the dewaxing of the fraction, whose boiling point is over 350 deg.C, by solvent, the viscosity index of the base oil is up to 130-190.