The adsorption mechanisms of cadmium on montmorillonite were investigated and the effects of different kinds of humic acid on adsorption mechanisms were revealed.It was found that adsorption amount of Cd2 increased as pH value of ambient solution increased.After humic acid added,the adsorption of Cd was logged because humic acid adsorptions took precedence of Cd2 .Then co-adsorptions of Cd2 were carried through between humic acid and montmorillonite. So the quantity of adsorption was greater than adsorption without humic acid.In addition,the adsorption mechanisms were related to the dose and its added manner of humic acid.