In　order　to　evaluate　seismic　performance　of　fiber　reinforced　polymer　(FRP)　confined　reinforced　concrete　(RC)　bridge　piers　with　hollow　section　under　horizontal　bidirectional　earthquake　action,　the　horizontal　bidirectional　quasi-static　test　was　carried　out　on　10　FRP　confined　RC　bridge　piers　with　rectangular　hollow　section.　The　failure　modes,　seismic　performance　parameters　and　effective　FRP　tension　strain　of　specimens　were　analyzed.　The　effects　of　slenderness　ratio,　wall　thickness,　axial　compression　ratio,　FRP　confining　parameters　and　strengthening　plans　on　failure　mode　and　seismic　performance　of　specimens　were　studied.　Based　on　experimental　results　and　present　computation　models　of　effective　FRP　tension　strain,　the　main　influencing　parameters　for　effective　FRP　tension　strain　were　determinated.　And　an　improved　FRP　effective　tension　strain　formula　was　presented　for　FRP　confined　bridge　piers　with　hollow　section　under　horizontal　bidirectional　earthquake　action.　The　results　show　that　dissipated　energy,　limit　deformation　and　ductility　of　confined　hollow　section　bridge　piers　are　improved　by　FRP　confining　within　plastic　hinge　region;　and　the　calculated　FRP　effective　ultimate　tension　strains　obtained　by　the　new　formula　are　well　agreed　with　experimental　results.