Abstract: The effect of microwave on the substitution of sodium element for calcium element in Ca montrmorillonite was studied. The exchange capacity of Na montmonillonite was determined by means of changing conditions, such as the treating time, the treating stage and the phase of montmonillonite. The result shows that treating by microwave is an excellent method for activating this reaction, the montmonillonite treated in solid phase is superior to that treated in suspended phase, treating before purifying process is beneficial not only to activation of this substitution but also to operation of the test; furthermore, microwave treating can increase the rate of this reaction apparently.