Marine　reinforced　concrete　constructions　(suspended　tunnels,　undersea　pipelines,　and　cross-sea　bridges)　are　inherently　at　risk　from　underwater　explosions　due　to　the　rising　incidence　of　worldwide　terrorism.　Sea-crossing　bridges　are　as　an　important　land-sea　connection　channel,　whose　anti-explosion　performance　cannot　be　ignored.　In　this　paper,　the　dynamic　response　and　damage　mechanism　of　piers　of　sea-crossing　bridge　under　underwater　explosion　loads　are　studied　by　the　arbitrary　Lagrangian-Eulerian　(ALE)　method.　Firstly,　the　correctness　of　the　explosive　load　and　reinforced　concrete　material　models　is　verified　by　the　Zamyshlyaev　formula　and　underwater　explosion　test,　respectively.　Secondly,　the　finite　element　(FE)　model　of　a　pier　under　an　underwater　explosion　load　is　established.　Taking　the　residual　vertical　bearing　capacity　of　the　pier　as　the　performance　index,　the　damage　evaluation　method　and　four　damage　levels　of　the　pier　under　explosion　load　are　put　forward.　The　study　of　different　parameters　such　as　explosive　weight,　explosion　location,　explosion　height,　and　explosion　distance　shows　that　the　damage　to　the　pier　is　the　most　serious　when　the　detonation　point　is　directly　below　the　projection　of　the　pier　cap.　The　residual　bearing　capacity　of　the　pier　falls　exponentially　as　explosive　weight　increases.　Different　detonation　heights　have　significant　effects　on　the　damage　to　the　pier.　Additionally,　it　is　found　using　the　explosion　vulnerability　analysis　approach　that　the　pier　is　very　susceptible　to　collapse　when　the　explosive　weight　is　350　kg.