The　dispersing　effect　of　superplasticizer　is　closely　related　to　its　adsorption　behaviors　on　the　surface　of　cement　particles　or　the　hydrates.　But　the　relationship　between　the　adsorption　amount　of　superplasticizer　and　the　fluidity　of　cement　paste　seems　uncertain.　To　investigate　the　relationship　between　the　adsorption　amount　and　the　fluidity　of　cement　paste,　three　groups　of　cements　with　designed　compositions　and　C(3)A　mineral　were　prepared　in　lab.　Four　types　of　superplasticizer　were　used　to　measure　the　adsorption　on　various　cements.　The　corresponding　zeta　potential　of　cement　particles　with　superplasticzers　and　the　fluidity　of　cement　pastes　were　tested　and　analyzed.　It　was　found　that　the　adsorption　amount　of　superplasticizer　was　inversely　related　to　the　fluidity　of　cement　paste　for　a　given　superplasticizer.　The　zeta　potential　of　cement　particles　in　the　paste　was　proportional　to　the　adsorption　amount　of　superplasticizer.　The　adsorption　amount　of　different　superplasticizers　at　the　isoelectric　point　in　C(3)A-H2O　system　was　determined.　The　meaning　of　the　＂adsorption　amount＂　was　discussed.　The　author　proposed　that　the　superplasticizer　in　cement　paste　should　include　three　parts,　and　the　role　of　each　part　was　discussed　according　to　test　results　and　analysis.