Abstract: The results of normal doublehydrometer test,pinhole test, crumb test,test for anion of solube salts of pore water and test for percentage of exchangeable sodium are always different. Through the study on the dispersive clay of the core wall of a dam,the reasons responsible for the disagreement are analyzed on basis of dispersive mechanism and standard of judgement. And,the quantitative standard of judgement must be studied especially for salinized soil in order to draft and implement the specification of dispersive clay test.