Failure criterion of saturated soft clay is studied under cyclic loads through different experiments. A large number of cyclic torsional shear and cyclic triaxial tests on saturated soft clay under unconsolidated undrained condition are conducted. From the test result analysis, it is seen that the failure of saturated soft clay under static and cyclic loads satisfies Mises criterion. The result from different test stress states is not related to the test stress states or confining pressures. It can be applied in general stress states. Then according to the Mises criterion, the equivalent relationship on failure moment between the test stress state and the general stress state can be established. So the cyclic mechanics characteristics of saturated soft clay at failure moment are clarified in this paper. Furthermore, a theory basis is provided for using pseudo-static elasto-plastic cyclic strength model to evaluate cyclic bearing capacity.