This　research　delves　into　the　characterization　of　the　ultrasonic　transmission　coefficient　pertaining　to　various　types　of　bonding　defects　in　Fiber-Reinforced　Polymer　(FRP)-bonded　structures.　Initially,　an　ultrasonic　transmission　coefficient　calculation　model　for　FRP-bonded　structures　in　a　water　immersion　environment　is　established.　This　model　is　used　to　analyze　the　variation　in　the　ultrasonic　transmission　coefficient　under　different　defect　types,　namely　intact　bonding,　interfacial　slip,　and　debonding　defects.　Subsequently,　a　frequency　domain　finite　element　analysis　model　of　FRP-bonded　structures　with　different　defect　types　is　constructed.　The　simulation　validates　the　accuracy　of　the　theoretical　analysis　results　and　concurrently　analyzes　the　variation　in　the　transmission　signal　when　the　defects　alter.　Lastly,　an　experimental　platform　for　water　immersion　ultrasonic　transmission　measurement　is　set　up.　The　transmission　signals　under　different　defect　types　are　extracted　through　experiments　and　evaluated　in　conjunction　with　theoretical　calculations　to　assess　the　types　of　bonding　defects.