Abstract: The swelling deformation properties of expansive rock during moisture absorption are studied by means of the expansion ratio tests. Through the swelling force tests, the influential factors are analyzed, and several empirical formula are deduced. According to the expansion ratio tests, the expansive rock has a positive linear correlation with its dry density, and negative linear correlation with its initial water content. The swelling force tests indicate that the general swelling force increases with the dry density and decreases with the initial water content. Moreover, the boundary constraint has significant impact on the general swelling force, and slight increase of expansion strain will cause dramatic decrease of the general swelling force.