Seawater　sea　sand　concrete　(SWSSC)　is　considered　a　potential　solution　to　the　shortage　of　river　sand　and　freshwater　resources　in　the　coastal　and　island　regions.　Under　the　marine　environment,　the　sulfate　ions　in　the　seawater　and　sea　sand　are　detrimental　to　the　properties　of　concrete.　Due　to　the　lack　of　systematic　research　on　the　sulfate　attack　characteristics　of　SWSSC　exposed　to　different　marine　conditions,　this　study　compare　the　sulfate　resistance　between　SWSSC　and　freshwater　desalinated　sea　sand　concrete　(FDC)　under　full　immersion,　semi　-immersion,　and　dry　-wet　cycle　exposure　through　the　compressive　strength,　sulfate　ion　distribution,　and　microstructural　changes　after　erosion.　The　findings　showed　that　among　the　three　different　exposure　conditions,　the　damage　in　SWSSC-F　(fully　immersion)　was　more　severe　than　that　in　SWSSC-S　(semi　-immersion)　and　SWSSC-DW　(dry　-wet　cycle).　The　SO42-　concentration　in　inner　SWSSC-F　was　9.3%　and　21.3%　higher　than　that　in　SWSSC-DW　and　SWSSC-S,　respectively.　The　microstructural　analysis　indicated　that　the　higher　amount　of　sulfate　attack　products　and　the　leaching　of　Ca2+/OH-　in　SWSSC-F　significantly　damaged　its　microstructure.　Besides,　carbonation　and　physical　crystallization　in　SWSSC-S　and　SWSSC-DW　also　refined　their　pore　structure,　thus　enhancing　their　sulfate　resistance.　SWSSC　showed　better　sulfate　resistance　than　FDC　under　different　marine　exposure　conditions　in　terms　of　lower　erosion　product　content　and　better　pore　structure　distribution　after　12　months　of　erosion.　The　formation　of　Friedel＇s　salt　in　SWSSC　suppressed　the　formation　of　expansion　products　and　reduced　the　erosion　damage　of　concrete　by　SO42-.