The method of slope stability analysis based on the assumption distribution of normal stresses over the slip surface is a progress of limit equilibrium theory. To obtain a reliable safety factor

it is essential to analyze the composition and assumption pattern of normal stresses over slip surface of slope which are dependent upon the body and inter-slice forces. Examples are given to analyze the distribution and contribution components of normal stresses over the slip surface under different assumptions of inter-slice forces. The results show that: Contribution component of slide body forces (including slope external forces) is dominant; and inter-slice forces are smaller contribution component. The safety factor is insensitive to the distribution of normal stresses over the slip surface. So

it is not necessary to demand for the accordance between assumption normal stresses distribution and real normal stresses distribution over the slip surface. Then

the assumption distribution of normal stresses over the slip surface could constitute by the contribution component of body forces

chosen as the kernel function

and the contribution component of inter-slice forces which could be approximated by a modifying function with two undetermined parameters. The research results have disciplined the assumption patterns of normal stresses

and have practical and theoretical value.