Abstract: Microcapsule self-healing technology can be applied to the healing of micro-damages in solid materials. The core materials selected in the existing research generally have the phenomenon of curing volume shrinkage, which cannot effectively fill the damaged sites, and affects the integrity and mechanical strength of the material after healing. Drawing on existing experience, a liquid expansion monomer with curing volume expansion was prepared and mixed benzoxazine with basically constant curing volume as the microcapsule core materials. By measuring the shrinkage/expansion rate and breakdown field strength of the cured products of the core materials, it was determined that the mixing mass ratio of benzoxazine and the expansion monomer in the core material was 10:3. The molecular dynamics simulation results show that the chemical compatibility between the core materials cured products and the epoxy resin matrix is good. The core material can be effectively cured under the separate or combined action of heat and light, and the volume expansion rate after curing is about 1.6%, which can effectively fill the damaged part, and has good breakdown strength. It is a potential microencapsulated anti-shrinkage curing core material used in self-healing epoxy resin.