Abstract: Based on ameliorative experiment about swelling energy measurement of Nanning expansive soils, new technique of making soil samples and principle of work-energy, experimental investigation and theoretical derivation are done from the perspective of the energy. The relationship between Nanning expansive soils" swelling potential and initial water content, initial dry density are discussed. Test shows that static force compacting work and swelling released energy are all inversely related to initial water content. There are rectilinear relationships between compacting work, swelling energy and density. Moreover, density is the main influential factor of compacting work and swelling energy.