Abstract: By extraction-flocculation combined process, the regeneration of spent lube oil was investigated using cyclohexane-isopropanol mixed solvent as extraction agent and KOH solution as flocculant. The base oil fractions in the feed were recovered at the optimal process conditions: cyclohexane to isopropanol ratio of 1:2, KOH solution concentration of 15%, KOH solution to organic solvents ratio of 7:1, solvent to oil ratio of 2:1, refining temperature of 45℃, refining time of 30 min, and the base oil yield is 83.4％. The regenerated lubricating oil is clear light yellow in color, the viscosities at 40℃ and 100℃ are 17.58 mm2/s and 4.11 mm2/s, respectively. The base oil has the viscosity index of 139, the acid value of 0.023 4 mgKOH/g, flash point of 234 ℃, and the solidifying point of -17 ℃. The performance index of the reclaimed oil is dramatically improved.