Using　glass　fibre-reinforced　polymer　(GFRP)　bars　to　reinforce　seawater　sea-sand　concrete　(SWSSC)　is　a　feasible　way　to　replace　traditional　concrete　structures.　Thus,　this　paper　aims　to　understand　the　shear　response　of　GFRP　bar-reinforced　SWSSC　(GFRP-SWSSC)　deep　beams.　Experimental　and　numerical　programs　were　carried　out　on　four-point　shear　tests　of　GFRP-SWSSC　deep　beams　without　stirrups.　Seventy　specimens　were　tested　to　investigate　the　effects　of　key　parameters　on　shear　responses,　including　concrete　categories,　seashell　content,　section　heights,　and　GFRP　bar　diameter.　The　test　results　indicated　that　the　cracking　strength　of　GFRP-SWSSC　deep　beams　was　slightly　higher　than　ordinary　concrete　deep　beams.　The　increased　section　height　of　GFRP-SWSSC　deep　beams　and　the　decreased　shell　content　remarkably　enhanced　the　stiffness　and　shear　ultimate　strength.　The　corresponding　finite　element　model　(FEM)　of　GFRP-SWSSC　specimens　was　established　and　validated　by　comparison　with　test　results.　Further,　three　guidelines　predictions　for　the　shear　strength　of　GFRP-SWSSC　beams　were　too　conservative.　The　new　design　formulae　derived　from　modified　tension-compression　theory　were　put　forward　to　evaluate　the　shear　strength　of　GFRP-SWSSC　deep　beams,　and　the　comparisons　demonstrated　that　the　proposed　design　formulae　achieved　sufficient　accurate　predictions　for　practical　engineering.　Based　on　research　on　shear　performance,　the　hybrid　GFRP-SWSSC　structure　is　a　feasible　solution　to　resource　shortages,　which　provides　a　promising　application　prospect　in　marine　engineering.　©　2024　The　Authors