This　paper　studied　the　mechanical　properties　and　electromagnetic　shielding　effectiveness　of　cement　paste　(CP)　mixed　with　fly　ash　and　slag.　With　pure　CP　as　the　control　group,　10%,　20%,　and　30%　cement　contents　were　replaced　by　fly　ash　and　slag.　Then　the　compressive　and　flexural　strength　of　the　samples　were　tested.　Wet　resistance　and　dry　resistance　of　samples　were　tested　by　the　four-probe　technique.　The　electromagnetic　shielding　effectiveness　of　the　sample　in　the　3.94　GHz-5.99　GHz　band　was　tested.　Finally,　based　on　the　mercury　intrusion　porosimetry　(MIP)　test　and　backscattered　electron　and　energy-dispersive　X-ray　spectroscopy　(BSE-EDS)　test,　the　impact　mechanism　of　fly　ash　and　slag　on　the　electromagnetic　properties　of　CP　was　expounded　from　the　pore　structure　and　element　distribution.　The　results　show　that　with　the　increase　of　fly　ash　or　slag,　the　strength　of　the　sample　decreased.　Mineral　admixtures　had　little　effect　on　wet　resistance,　while　dry　resistance　showed　an　increasing　trend　with　the　increase　of　mineral　admixture　content.　The　reflection　loss　had　the　greatest　impact　on　electromagnetic　shielding　effectiveness.　With　the　increase　of　mineral　admixture　content,　the　reflection　loss　and　multiple　reflection　loss　of　the　sample　increased,　but　the　absorption　loss　decreased.　The　reason　for　the　effect　of　compounding　different　proportions　of　fly　ash　and　slag　on　the　electromagnetic　shielding　effectiveness　of　CP　is　mainly　due　to　the　change　in　the　proportion　of　mesopores　with　an　aperture　less　than　100　nm　and　the　content　of　metallic　elements　(e.　g.　Fe)　in　the　specimens.