The experimental study on the adsorption capacity of montmorillonite, kaolinite and illite for Cu2+,Pb2+, Zn2+, Cd2+and Cr3+was conducted under the conditions of pH=4,t=23℃and very low concentrations of heavy metals. In this study, some means were used for the purpose of keeping the original concentrations of heavy metals unchanged and increasing the amount of heavy metals by adding heavy metals_bearing solution into the reaction systems. The adsorption capacities of the three clay minerals for the five heavy metals are found to be in order of montmorillonite > illite > kaolinite. Their adsorption capacities are mainly controlled by their CEC. XRD results of Cu_montmorillonite and Cr-montmorillonite show that Cu2+and Cr3+have entered the interlayer of montmorillonite by cation exchange with Ca2+. Also, adsorption capacities of each mineral are different for different heavy metals: the adsorption capacities of montmorillonite, kaolinite and illite for different heavy metals are in order of Cr3+>Cu2+>Zn2+>Cd2+>Pb2+, Cr3+>Pb2+>Zn2+>Cu2+>Cd2+and Cr3+>Zn2+>Cd2+>Cu2+>Pb2+respectively.