AC　impedance　is　a　new　method　to　study　the　changes　of　pore　structure　and　the　hydration　degree　during　the　hydration　and　hardening　process　of　cement　paste　by　the　change　of　the　electrochemical　parameters.　Employing　AC　impedance　method,　we　studied　the　hydration　and　hardening　process　of　cement　paste　with　fly　ash　and　slag,　and　analyzed　the　influence　of　different　hydration　age,　water-binder　ratio　and　mineral　admixture　on　the　impedance　parameters.　Moreover,　we　compared　the　results　with　those　by　the　conventional　porosity　testing　method　and　X-ray　diffraction　method.　The　results　showed　that　AC　impedance　could　be　taken　as　a　new　technology　in　cement　and　concrete　research.