The　adsorption　rate,　water　absorption,　volume　swelling　capacity　of　4　kinds　of　clay,　and　the　interlayer　spacing　of　montmorillonite　were　tested.　The　adsorption　capacity　and　mode　of　polycarboxylate　superplasticizer(PCE)　on　different　clays　were　studied.　The　volume　change　of　solid　and　liquid　phase　in　fresh　concrete　before　and　after　adsorbing　PCE　by　clay　was　calculated.　The　inhibition　mechanism　of　clay　on　applying　performance　of　PCE　was　explored.　The　results　show　that　the　adsorption　of　PCE　on　clay　is　higher　than　that　on　cement,　and　adsorption　capacity　of　montmorillonite　is　the　strongest　of　all.　The　side　chain　of　PCE　molecular　is　adsorbed　into　interlayers　of　montmorillonite,　which　increases　the　interlayer　spacing(d(001))　of　montmorillonite　from　1.443nm　to　1.863nm.　Clay　adsorbs　more　PCE　and　thus　reduces　the　effective　content　for　dispersing　action.　The　volume　of　clay　expands　after　absorbing　water,　increasing　the　solid　phase　volume　and　decreasing　the　liquid　phase　volume,　and　finally　worsening　the　workability　of　fresh　concrete.