The circular slices method is one of the normal method for analyzing stability of slope which assumed the stabilities of individual slice is equal and equaled to that of whole slope, and belongs to an imprecise limit equilibrium method of rigid body with some irrationality. With a simple slope as research model, the circular slices method is improved. Postulating the slices can transfer internal force each other and the stabilit ies of individual slice are not equal, the differentiating condition of slope stabilization states is put forward via studying the transmission principle of slices force interacted by each other, and the theory formula calculating interact ion forces of individual slices is deduced at a stable slope. Based on above, the theory formula calculating stability factor of whole slope from the stability factors of individual slice is also deduced according to the principle of disjoin- join and the principle of weight weighted average of sliding factors.