Abstract: According to the Mohr Coulomb yield criterion, the stress field of a semi infinite slope is derived under a vertical uniform load q on the top of the slope.It is indicated that elastic and elasto plastic states would occur in the slope. When q is less than the critical load q p ,the slope is in elastic state. If q equals q p ,the slope is in critical state, and the plastic deformation may occur beyond the critical angle. With the increase of q , the plastic zone would extend, and the slope is in the elasto plastic state. If q equals limit load, the slope is in limit equilibrium state. The slope may be divided into three zones. Some charts of the critical angle, the critical and limit load coefficients are presented in this paper.