The present invention discloses a modified bismaleimide resin and preparation method thereof; under conditions of N,N-dimethylformamide serving as a catalyst, biomass-based 2,5-furandicarboxylic acid and thionyl chloride are acylated to obtain 2,5-furan diformyl chloride, which is then dissolved in dichloromethane with a biomass-based eugenol; under tertiary amine conditions an esterification reaction takes place, and a fully biomass-based bis(4-allyl-2-methoxyphenyl)furan-2,5-dicarboxylic acid ester is thus obtained; same is used for preparing a modified bismaleimide resin. The bismaleimide resin prepared by the present invention has excellent thermal properties and rigidity; the preparation method uses 2,5-furandicarboxylic acid from biomass as well as eugenol; the raw materials are green and environmentally friendly and renewable; the invention also has the feature of a simple production process, and has broad prospects for application in such fields as aeronautics and astronautics, electronic information, electrical insulation.