By means of the vector sum method and strain-softening constitutive model, a method for progressive failure analysis of strain-softening slopes is developed, which can show the processes of variations of the strain-softening slope safety factor, strength parameters, and failure state of slope and slip. Based on this, progressive failure progress of slope with strain-softening behavior can be simulated. Numerical results are compared to those of the limit equilibrium methods, showing the validity of the proposed method. It is shown that the vector sum method safety factor are in between peak and residual safety factors by the limit equilibrium method; the strength parameters of the main part of slip surface are at the peak value, and the other at the residual value; the proposed method compensates for the defect of the traditional limit equilibrium methods failing to provide a realistic safety factor of slope with strain-softening behavior. The strength weakening zone is found to be consistent with the failure zone in the slope. In the shearing process, the strain-softening behavior first occurs at the toe of the slope, and the strength parameters reduce to the residual value at the toe of the slope; then new strain-softening behaviors occur at the adjacent zone and then enter the residual state; finally the progressive failure develops from the toe of slope to the top of the slope. As the process continues, the progressive failure gradually develops and the safety factor decreases until the end of the progressive failure is reached. The safety factor increases with the increase of residual soft parameter, and the position of critical slip surface moves towards shallow, resulting in an increase of the vector sum method safety factor.