The　search　for　construction　materials　that　contribute　to　5G　signal　transmission　is　important　for　the　development　of　modern　communication　technologies.　In　this　paper,　the　mechanical　properties　of　white　Portland　cement　(WPC)　paste　mixed　with　basalt　fiber　(BF)　were　analyzed　and　its　electromagnetic　properties　were　fully　investigated.　First,　the　fluidity　and　strength　of　WPC　pastes　with　different　BF　contents　were　tested.　Subsequently,　the　electromagnetic　parameters　of　WPC　paste　samples　were　tested　in　the　frequency　band　of　3.94　GHz-5.99　GHz,　and　their　electromagnetic　transmission　properties　were　calculated.　Finally,　the　mechanism　of　BF　affecting　the　strength　and　electromagnetic　transmission　performance　of　WPC　pastes　was　profiled　using　scanning　electron　microscopy　(SEM)　and　mercury　intrusion　porosimetry　(MIP).　The　results　show　that　BF　can　reduce　the　fluidity　of　WPC　pastes.　With　the　increase　of　BF　doping,　the　strength　of　WPC　paste　rises　and　then　decreases,　and　reaches　the　maximum　strength　when　the　volume　content　of　BF　is　0.6%.　With　the　increase　of　BF　content,　the　electromagnetic　wave　reflection　rate　of　WPC　paste　decreases,　but　the　absorption　and　transmission　rate　increases.　The　bridging　effect　of　BF,　etc.　improves　the　strength　of　the　paste.　In　WPC　pastes,　with　the　increase　of　BF　doping,　the　increase　of　electromagnetic　wave　absorption　rate　is　smaller　than　the　decrease　of　reflection　rate,　which　leads　to　the　improvement　of　electromagnetic　transmission　performance.