Aiming at the discontinuity of hard crust outside the toe of embankment(such as fishpond, etc. ), through theoretical analysis and numerical simulation, the failure mode of a soft soil layered foundation with continuous and discontinuous hard crust has been compared and analyzed under the embankment load, and a judgment parameter of failure mode, namely the critical distance L_cr, is proposed to distinguish between the general shear failure mode and the local shear failure mode. With the principle of orthogonal test, factors that influence L_cr have been analyzed, and each factor is given in order of sensitivity. Then, using the iterative method with stepwise regression, mathematical formulas of upper(L_crU)and lower(L_crD)limits of the critical distance are given respectively, and their reliability are demonstrated by checking an engineering project. The results indicate that the failure mode of soft soil foundation with continuous hard crust is general shear failure. When the hard crust layer is discontinuous, the failure mode is general shear failure if the distance between discontinuous section and embankment toe is less than L_crU or higher than L_crD, and local shear failure if the distance is between L_crU and L_crD. The thickness of hard crust layer is the main factor to L_cr and the secondary factor is the thickness of soft soil layer, while the influence caused by the internal friction angle and the cohesion of hard crust layer is smaller.