Abstract: In this paper, two new terms of the stress couples acting on the principal shear planes and their actions are proposed and a new failure criterion is given to amend the twin-shear unified failure criterion based on the considerations that the effects of all the three stress couples acting on the principal shear planes of the dodecahedral element should be taken into account in the establishment of the failure criterion. Theoretical analyses of the loci on π plane and the loci on (σ1 ?σ2) plane, the Mohr circles on (σ ?τ) plane, the effective curves with the intermediates principal stress, and the directions of the failure surface have shown that this criterion can basically reflect the nonlinear failure and strength characteristics of the geomaterials and avoid the defect of two broken angles existed in the twin-shear unified criterion under some stress states. Finally, this new criterion is used to analyze the earth pressure of retaining wall.