A proton exchange membrane comprising modified hyper-branched polymer is disclosed. The proton exchange membrane includes 85-90 wt % of sulfonated tetrafluorethylene copolymer and 15-10 wt % of modified hyper-branched polymer. The modified hyper-branched polymer comprises the bismaleimide (BMI)-based hyper-branched polymer, and parts of the chain ends of the hyper-branched polymer are sulfonated by the sulfonic compound. Also, the modified hyper-branched polymer and sulfonated tetrafluorethylene copolymer are interpenetrated to form an interpenetrating polymer. Furthermore, the modification step could be performed before or after forming the interpenetrating polymer. For example, the sulfonation is proceeded after forming the interpenetrating polymer. Alternatively, the sulfonation of the hyper-branched polymer could be proceeded before the formation of the interpenetrating polymer.