C3S　(tricalcium　silicate)　pastes　with　water-cement　ratio　(W/C)　of　0.23,　0.3,　0.4　and　0.5　were　designed,　and　the　influence　of　the　dielectric　properties　of　C3S　paste　were　quantitatively　analyzed.　The　results　show　that　when　the　W/C　is　0.23,　the　real　part　of　permitivity　of　the　C3S　paste　is　the　smallest.　With　increases　of　the　W/C,　the　real　part　of　permitivity　of　the　C3S　paste　decrease,　and　the　loss　tangent　increases.　The　real　part　of　permitivity　of　C3S　paste　decreases　with　the　increase　of　Ca(OH)2　and　pore　phases,　and　increases　with　the　increase　of　C3S　and　CSH　gel　phase.　The　permitivity　of　C3S　paste　decreases　most　due　to　increase　pore　phase　(about　4　times　that　of　Ca(OH)2　phase),　and　increases　most　due　to　increase　CSH　gel　phase　(about　6.6　times　that　of　C3S　phase).　The　dielectric　weight　coefficient　proposed　in　this　study　can　well　predict　the　changing　trend　of　the　real　part　of　permitivity　of　C3S　pastes　with　different　W/C.　Finally,　based　on　the　Thermogravimetric　analysis　(TGA),　Scanning　electron　microscope　(SEM),　Mercury　intrusion　porosimetry　(MIP),　N2　adsorption　and　29Si　magic　angle　spinning　nuclear　magnetic　resonance　(29Si　NMR)　test　results,　the　reasons　of　electromagnetic　loss　changes　of　C3S　pastes　with　different　W/C　were　analyzed　from　the　molecular　structure　of　CSH　gel,　the　crystalline　products　and　the　pore　structure　of　C3S　paste.