The bonding mechanism between water-based UV curable ink and active groups on paper’s fiber during curing process was studied in this paper. Low viscosity water-based UV-cured resin was synthesized by epoxy resins, epoxy diluent, acrylic acid and maleic anhydride in the presence of catalyst. The viscosity of the synthesis system and synthetic products were significantly reduced when epoxy diluent was added to replace parts of the epoxy resin. Epoxy diluent was very useful in reducing the viscosity of the product, but over-dose would have negative effects on the quality of the cured film. The water-based epoxy acrylate prepolymer was used as the substitution for the ink to investigate the binding mechanism between the active groups of prepolymer and fiber under UV irradiation. The prepolymer and photoinitiator were mixed and the mixture was diluted to an appropriate viscosity by a small amount of water, then printed on the paper by the method of analog printing and curred by UV curing machine. The printed paper was used to extract lignin by enzymatic/mild acidolysis. FT-IR was used to characterize the changes of the active groups in lignin. The results showed that the changes of active groups in lignin were founded in the existence of ultraviolet and photoinitiator, which consistent with the change of double bonds in prepolymer. The free radicals produced by photoinitiator in curing process not only promoted the double bonds to polymerize, but also accelerated the active groups of lignin binding. Experiments show that chemical bonds exist between them.