As　a　high-quality　building　material　exhibiting　excellent　toughness　and　durability,　ultrahigh-performance　concrete　(UHPC)　is　increasingly　being　used　in　the　construction　industry　and　as　building　reinforcement.　During　the　reinforcement　of　existing　concrete　structures　with　UHPC,　their　interface　is　the　weakest　part　of　a　structure.　Interface　bonding　ensures　the　operation　of　two　types　of　materials　together.　However,　existing　studies　rarely　report　the　bonding　of　the　UHPC-normal　concrete　(NC)　interface.　Herein,　the　existing　test　methods　and　interface　bonding　mechanisms　are　summarized.　Subsequently,　the　differences　among　relevant　design　codes　are　investigated　by　comparing　different　theoretical　formulas.　Important　influencing　factors　of　the　reinforcement　method,　namely,　interface　roughness,　fiber　type　and　content,　interface　agent　type　and　content,　moisture　content,　existing　concrete　strength,　cementitious　material　content,　curing　conditions,　freeze-thaw　cycles,　and　chloride　ions,　are　also　considered.　Further,　the　enhancement　mechanism　of　the　characteristics　of　the　UHPC-NC　interface　is　clearly　described.　Finally,　the　shortcomings　and　application　prospects　of　the　interfacial　bonding　properties　are　highlighted.