Certain amounts of calcium montmorillonite sodium montmorillonite and sodium carbonate were mixed into Yangling loess to prepare samples.The samples'' dispersibility and pH were studied by pinhole test crumb test and pH test in order to analyse factors that affect clay''s dispersion.The results show that the content of montmorillonite and sodiumion in Yangling loess is low and belong to non-dispersive clay. When mixed with a certain amount of sodium montmorillonite or sodium carbonate,it became dispersive clay,and the greater the amount of sodium montmorillonite or sodium carbonate it was mixed with,the more obvious its dispersibility became and the higher pH it would has,but when mixed with a certain amount of calcium montmorillonite,it was still non-dispersed clay,and the greater the amount of calcium montmorillonite it was mixed with,the more slowly its disintegration became and the lower pH it would has.Sodium montmorillonite sodiumion and pH have significant effects on clay''s dispersion.The nesessary condition for creating the dispersive mechanisms of soil lie in more sodiumion and stronger alkalinity(pH＞8.5) in the soil. The clay will generate dispersion as long as it contains more sodiumion and pH＞8.5.