The　application　of　seawater　and　sea　sand　concrete　(SWSSC)　is　beneficial　for　marine　engineering,　but　the　impact　of　aggregate　gradation　on　its　alkali-silica　reaction　(ASR)　remains　poorly　understood.　This　study　aims　to　bridge　this　gap　by　analyzing　ASR　products,　pore　characteristics　and　expansion　rate　of　specimens.　The　test　results　reveal　that　ordinary　concrete　(OC)　exhibits　an　inhibitory　effect　on　ASR　in　comparison　with　to　SWSSC.　The　14-day　expansion　of　ordinary　concrete　and　SWSSC　with　the　same　aggregate　gradation　are　0.130　%　and　0.212　%,　showing　potential　and　high　risk　of　ASR,　respectively.　Moreover,　particle　size　and　gradation　of　aggregate　are　the　key　factors　influencing　the　ASR　degree　of　SWSSC.　Compared　with　coarser　aggregate,　specimens　with　finer　aggregate　consume　more　K+　and　Ca2+　ions,　generate　more　ASR-P1,　form　less　porosity,　and　produce　a　larger　expansion.　Additionally,　specimens　with　gap-graded　aggregates,　as　opposed　to　those　with　uniform　or　continuous　gradation,　show　greater　consumption　of　K+　and　Ca2+　ions,　increased　ASR-P1　formation,　more　harmful　pore　formation,　and　a　larger　expansion.　These　results　offer　insights　into　optimizing　aggregate　gradation　to　reduce　ASR　in　SWSSC　and　improve　its　durability.