5G　signal　transmission　can　be　seriously　blocked　by　cement-based　materials,　so　it　is　very　important　to　improve　the　electromagnetic　transmission　performance　(ETP)　of　cement-based　materials.　Carboxylated　nanocrystalline　cellulose　(NCC)　is　used　to　prepare　Ordinary　Portland　cement　paste　with　high　ETP.　The　water-cement　ratio　and　NCC　content　of　the　cement　paste　are　0.5　and　0–4%　respectively.　The　test　results　show　that　the　ETP　of　cement　paste　increases　by　13.9%–90.6%,　but　the　compressive　strength　of　the　sample　decreases　by　7.3%–87.6%.　The　2%　of　NCC　content　causes　the　ETP　of　cement　paste　increases　by　75.6%,　while　the　compressive　strength　only　decreases　by　14.6%.　The　reasons　for　improvement　of　ETP　are　that　the　electrostatic　force　between　the　globule,　the　polymerization　degree　and　mean　chain　length　of　C–S–H,　the　total　volume　proportion　of　phases　(calcium　hydroxide,　ettringite　and　unhydrated　cement)　with　low　dielectric　loss　and　the　volume　proportion　of　the　no　harmful　pore　for　electromagnetic　energy　loss　are　increased,　the　conductivity　of　cement　pore　solution　and　the　content　of　water　are　decreased.　©　2023　Elsevier　Ltd