The　characteristics　of　seawater　sea　sand　concrete　become　a　recent　research　issue,　while　the　alkali-silica　reaction　(ASR)　of　seawater　sea　sand　concrete　is　still　unclear.　To　clarify　the　influence　of　supplementary　cementitious　materials　on　the　alkali-silica　reaction　characteristics　of　seawater　and　sea　sand　concrete,　the　cement-metakaolin-fly　ash-slag　cementitious　materials　were　designed　by　a　simplex　centroid　design　method.　The　effect　of　supplementary　cementitious　materials　on　the　ASR　products,　pore　structure,　pore　solution　pH　value,　alkali　ion　content　and　expansion　rate　of　seawater　and　sea　sand　concrete　was　investigated.　The　results　show　that　the　content　of　the　amorphous　product　ASR-P1(K0.52Ca1.16Si4O8(OH)2.84·1.5H2O)　and　the　crystalline　product　Na-shlykovite　(NaCaSi4O8(OH)3·2.3H2O)　in　seawater　and　sea　sand　concrete　are　inversely　proportional　to　the　content　of　active　SiO2　and　Al2O3　in　supplementary　cementitious　materials.　Among　the　seawater　and　sea　sand　concretes　with　different　cementitious　materials,　the　pH　value　of　paste　prepared　with　50%　cement+25%　metakaolin+25%　fly　ash　and　the　contents　of　Na+,　K+　and　Ca2+　are　the　minimum　values.　As　a　result,　the　content　of　ASR-P1　and　Na-shlykovite,　the　content　of　harmful　pores　and　multi-harmful　pores　are　the　minimum　values,　as　well　as　the　porosity　is　the　maximum　value,　thus　resulting　in　the　minimum　expansion　rate　of　the　paste　prepared　with　25%　metakaolin+25%　fly　ash　+50%　cement　at　14　d　and　28　d.　This　paper　can　provide　a　theoretical　basis　for　the　design　of　cementitious　material　composition　of　seawater　and　sea　sand　concrete,　and　improve　the　service　life　of　seawater　and　sea　sand　concrete　structure　in　marine　engineering.　©　2023　Chinese　Ceramic　Society.　All　rights　reserved.