The invention discloses a method for preparation of a lignin oligomer through selective reductive degradation. The method includes: taking nano ZrO2 loaded Pt (Pt/ZrO2) as a main catalyst, adopting Lewis acid as a cocatalyst, and conducting hydrogen reduction degradation of lignin in an alcohol/water medium to prepare the lignin oligomer with a high phenolic hydroxyl content. The method provided by the invention is simple, and the lignin degradation reaction process is environment-friendly and non-toxic, the Pt/ZrO2-Lewis acid composite catalytic system has the advantages of high catalytic activity, good lignin degradation reaction selectivity, high conversion rate (the highest phenolic hydroxyl value of the degradation product accounts for 97.5% of a total hydroxyl value, and the yield is94.3%) and the like, and can effectively inhibit the generation of solid residue in the degradation reaction process, and the prepared lignin oligomer can replace traditional fossil resources to be applied to synthesis of bio-based epoxy resin, phenolic resin, polyurethane and other environment-compatible green polymer materials.