The invention discloses a biomass-based epoxy resin and a preparation method thereof. The preparation method comprises that in the presence of N, N-dimethylformamide as a catalyst, 2, 5-furandicarboxylic acid and thionyl chloride undergo an acylation reaction to produce 2, 5-furandicarbonyl chloride, the 2, 5-furandicarbonyl chloride and eugenol are respectively dissolved in dichloromethane and undergo an esterification reaction under the condition of tertiary amine to produce bis(4-allyl-2-methoxyphenyl)-furan-2, 5-dicarboxylate, and unsaturated double bonds in the bis(4-allyl-2-methoxyphenyl)-furan-2, 5-dicarboxylate are epoxidized by m-chloroperoxybenzoic acid to form the biomass-based epoxy resin. The preparation method has simple processes, and utilizes 2, 5-furandicarboxylic acid and eugenol as raw materials. Compared with the bisphenol A epoxy resin based on petroleum and coal resources, the raw materials are environmentally friendly and reproducible, and is conducive to reduction of polymer production-caused consumption of non-renewable resources. The cured epoxy resin has excellent thermal performances and modulus and has a wide application prospect.