The　mechanical　properties　and　electromagnetic　transmission　properties　of　high　alumina　cement　(HAC)　paste　with　different　glass　powder　(GP)　contents　were　investigated　in　this　paper.　The　effects　of　hydration　phase,　unhydrated　phase,　GP　phase　and　pore　phase　on　the　dielectric　properties　of　HAC　paste　were　quantitatively　analyzed.　The　results　show　that　the　strength,　fluidity　and　setting　time　of　HAC　paste　decrease　with　the　increase　of　GP　replacement　rate.　The　real　part,　imaginary　part　and　loss　angle　tangent　of　dielectric　constant　decrease.　The　addition　of　GP　leads　to　a　reduction　in　reflectivity　and　absorptivity　of　electromagnetic　waves　in　the　paste,　while　increasing　transmittivity.　Furthermore,　the　real　part　of　the　dielectric　constant　of　each　phase　in　the　HAC　paste　follows　the　order:　hydration　product　phase　＞　unhydrated　phase　＞　GP　phase　＞　pore　phase.　With　an　increase　in　GP　content,　the　real　part　of　the　dielectric　constant　of　the　hydration　product　phase　increases.　Finally,　based　on　the　results　of　vector　network　analysis　(VNA),　mercury　intrusion　porosimetry　(MIP)　and　scanning　electron　microscopy　(SEM),　the　reasons　for　the　changes　of　mechanical　properties　and　electromagnetic　properties　of　HAC　paste　under　different　GP　replacement　rates　were　analyzed　from　the　aspects　of　phase　composition,　pore　distribution　and　microstructure.