In order to study the mechanical properties and structural properties of soft dredger fill under lateral deformation. Based on true triaxial and WF stress path apparatus, lateral unloading undrained tests were carried out. The results derived from true triaxial test, WF stress path test and routine triaxial shear test were analyzed. The contrastive conclusions are as follows: The stress-strain curve of true triaxial unloading test shows a softening behavior, which is different from the hardening behavior for that of conventional triaxial shear test. With the increase of initial confined pressure, the dilatancy of soil transfers from shrinkage to expansion. The structural yield stress of the unloading soil with true triaxial test method is dramatically larger than that with the latter two tests due to the effect of intermediate principal, which exhibits a nonlinear growth as the coefficient of intermediate principal bd stress jumps. The shear strength indexes of unloading soil with true triaxial test is larger than that with WF stress path test. Compared with the results of routine triaxial test, the internal friction angle of true triaxial test is bigger while the cohesion is smaller.