Abstract: Getting erosion is the characteristic of dispersive clay which would cause series of damages to hydraulic projects like dams. AlCl3•6H2O, MgCl2•6H2O, CaCl2 and CaO were selected as chemical modification materials of dispersive clay based on the mechanism of dispersivity. The judgments and comparisons of soil samples were made using pinhole tests and crumb tests. Tests show that with the modification materials selected above, the ability against erosion of dispersive clay was improved; and the dispersive clay would turn into non-dispersive. The results indicate that cations with higher valence state mixed into dispersive clay could reduce the diffusion layer by replacing sodium ions in soil particles surface or by lessening soil alkaline; as a result, it plays a role in modification. According to mechanism of dispersivity and the results of modification test, the chemical modification principles of dispersivity are put forward; modification materials contain cations with higher valence state or pH is acidic. Materials should environmental friendly and have lower price, and also facilitates the construction,

Key words: dispersive clay, mechanism of dispersivity, pinhole test, crumb test, chemical modification