Abstract: The properties of bentonite are influenced by the type and content of exchangeable cations. The content of single-type cations can be increased by purification, thereby improving the properties of bentonite (such as the properties of adsorption, dispersion and expansion). The Gaomiaozi (GMZ) bentonite was used as the tested materials. Purification of exchangeable cations was first carried out through the immersion-dialysis method, and the cations was exchanged by using NH₄Cl-C₂H₅OH solution. Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the species and content of exchangeable cations. The experimental results show that the use of dialysis to wash salt can significantly improve the soil sample recovery rate,which is above 96%, and the salt washing time is about 3 days. After the bentonite is repeatedly exchanged with the NH₄Cl-C₂H₅OH solution for 5 times, the exchangeable cations can be replaced completely.The exchangeable sodium percentages of GMZ bentonite was 72.12%, the exchangeable potassium percentage was 82.60%, and the exchangeable calcium percentage was 88.16%, respectively. The purification rate of single-type exchangeable cations has been greatly increased. The purification of bentonite by dialysis is simple and effective, which is worthy of further study.