Abstract: Based upon rock deformation characteristics and bounding surface model, a strain-softening law and its constitutive equation are established. In the equation, two difficult problems on solution and surface drifting are existed. First, after numerical approaches to softening problem were evaluated, an initial stress method is employed and then improved. It is called improved initial stress method which accelerate convergence. Secondly, various surface drifting updatings are compared and a good correction is selected. Correspondingly, the program called EPSF is developed. Finally a strain-softening analysis to a tunnel in Jinchuan is given.