Abstract: By using the trial stress return mapping algorithm, a user-defined material subroutine (UMAT) of the constitutive model of soil considering complex stress path is complied. The precision of the UMAT is tested by simulating triaxial compression tests and triaxial extension tests based on ABAQUS. Three-dimensional finite element analysis of excavating small diameter axisymmetric round foundation is carried out by means of the second-developed ABAQUS with the UMAT. The variations of the intermediate principal stress and the minimum principal stress and the laws of soil arch caused by the intermediate principal stress under the plane strain condition are studied.