Abstract: n over to study different water(deionized watertap water r fling water from the col preparaton pant an ciculated water ofthe coal lreparation plant hadness afc1ed to the slime foladion efect Powereach JC 20D1 conact angles measuing apparadus and JS4 mode microelectrophoresis apparatus and othes were aplied to anajze the weting contar angle ofth slime in diferent hardness waler medtum and the variation of -polenial and thn the comparison experiment of the stagereased fotaion was conducted The estuts showed tatin the producion pactces.waer hadhessofthe foatation would be high dferentwit th waler hadress o the fioalation increased,the -—OHf contenton the partice surace of h slime increased,theweabilit increased and iydrophobicty decveased the pric e cotact ang es of theslime would b reduced.The waler hardress iceased would comprss h double efecticlyers around th coal paricls.the , otentia ofthe parices in water woul be reduiced the bubles and the hyaraled layers betwe n thecoal parfic es wouldbe eail roken The conat dficity betwee thecal patices and bubles would be reduced Underthe same co dition when th sury mivedwith high hardness waet,the clean mineral production rate and the combustible material recovered rate would be higher than the slurry with low hardness water.