Abstract: No linear qualities of triaxiat tests results and direct shear tests results encourage a proper curve to be constructed to illustrate soils' limit equilibrium state based on Mohr envelope. With the application of elastic theory, equations are derived to calculate plastic range of ground under band-load operation, and then, critical load and plastic zone can be obtained. Several conclusions on the shape and size of plastic zone induced by band-load can be got after the comparison, which is performed between results respectively from the two methods. Even the difference between the shape and the size of the two kinds of plastic zone created by the same load is small and the two critical loads have the similar character, plastic zone increment with increasing upper load is quicker when the proposed method is applied.