UV-curable phosphorus-containing epoxy resin was synthesized with chain-extension of （3,4-epoxycyclohexyl）methyl-3,4-epoxycyclohexanecarboxylate （ERL4221） and 2-（6-oxido-6H-dibenz（c,e） （1,2）- oxaphosphorin-6-yl）-l,4-benzenediol （DOPO-HQ） at different stoichiometric ratios. The structures of these resins were characterized by IR and 1H-NMR. The influences of different phosphorus contents on the epoxy value of the epoxy resin, thermal properties, flame retardancy, and UV curing properties were investigated. The results showed that the thermal stability and flame resistance increased compared with those of the unmodified ERL4221 epoxy resin under the same conditions. When the phosphorus mass content was 1.5%, the limiting oxygen index （LOI） reached 24.9, vertical burning achieved V-1 levels, and had a higher light curing activity.