Abstract：The stage moistening deformation tests are performed for the compacted expansive soil in Ankang using improved triaxial apparatus. The experiment shows that the deformation of the expansive soil is swelling deformation under triaxial stress state with the same stress ratio in the immersion process. The soil deformation appears in specimen¢s every orientation，the deformations in the radial and axial directions behave swelling when stress is smaller. The axial direction expresses the compresses deformation and the radial direction expresses swelling deformation when stress is greater，but the deformation is very little. In moistening shear process，the deformation of the sample is chiefly volumetric expansion and volumetric changes is chiefly lateral deformation，and the axial direction deformation is smaller；the mathematical fittings are done for the experiments data，and the fitting formula has been verified. The results show that the experimental value agrees well with calculation value.
