The variation regularity of swelling pressure p and expansion ratio under 50 kPa pressure with dry density ，degree of saturation and water content w were investigated. The results show that:the relations between p

and

;and between p and can be illustrated in power exponent function；the variation of p and under various conditions can be better described by one or two factors that are w， ， ；in general，w is epuivalent to while high w； is equwalent to while lower w；and is equivalent to while certain w；there is a critical value of dry density，p decreases as increase when more than the critical value，otherwise the conclusion is opposite.