Epoxy resins generally refer to organic polymer compounds containing two or more epoxy groups in the molecule. Except for a few, their relative molecular mass is not high. The molecular structure of epoxy resin is characterized by the active epoxy group in the molecular chain. The epoxy group can be located at the end, in the middle or in a cyclic structure of the molecular chain. Because the molecular structure contains active epoxy groups, they can undergo cross-linking reactions with various types of curing agents to form insoluble and infusible polymers with a three-way network structure.