Expansive soil is a special clay with strong swelling and shrinking properties. It is of great significance to grasp the law of three-way expansion for the rational analysis of deformation and instability of expansive soil slope. Taking Nanning gray-white expansive soil as the test object, three-way expansion rate and expansion force tests under different conditions were carried out, revealing the influence of dry density, initial moisture content and external load on the expansion rate and expansion force. Tests show that the three-way swelling rate and swelling force are as follows: the two horizontal directions are basically the same, the vertical direction is greater than the horizontal direction; both decrease with the increase of the initial water content when the dry density is the same ; both increase with the increase of the initial dry density when the initial water content is the same; the lateral and vertical ratios of the swelling ratio both approach to 1 with the increase of the dry density or the initial moisture content; The three-way expansion rate is logarithmically linear with the three-way load, and the load has an inhibitory effect on the expansion; the lateral expansion force and the control lateral expansion rate have a good exponential relationship, indicating that the expansion force of the soil will be greatly reduced due to the expansion deformation.