The present invention discloses a biomass-based epoxy resin and preparation method thereof; under conditions of N,N-dimethylformamide as a catalyst, 2,5-furandicarboxylic acid and thionyl chloride are acylated to obtain 2,5-furan diformyl chloride; then it is dissolved with dichloromethane; under tertiary amine conditions an esterification reaction takes place, and bis(4-allyl-2-methoxyphenyl)furan-2,5-dicarboxylic acid ester is thus obtained; by means of meta-chloroperoxybenzoic acid, its unsaturated double bond is epoxidized to obtain a biomass-based epoxy resin. The process of the present invention is simple; the raw materials come from biomass 2,5-furandicarboxylic acid and eugenol; in comparison with bisphenol-A epoxy resin based on petroleum and coal resources, the raw materials are green and renewable, and are advantageous to reducing the consumption of renewable resources with regard to polymeric material. The obtained cured epoxy resin has excellent thermal properties and modulus, and has broad prospects for application.