Abstract: The conventional rock wedge stability analysis method proposed in textbooks actually involves an assumption that the shear forces applied on the failure planes are parallel to the line of intersection. Pan argued that the shear force does not necessarily act in such a way but would readjust to mobilize the maximum factor of safety. A new method that allows an input of various shear force directions is presented in this paper. By applying the limit equilibrium conditions a governing equation to calculate the factor of safety has been obtained, which permits a formal demonstration to confirm that a maximum factor of safety exists when the rock wedge dilates at values of friction angles to the left and right failure planes respectively along the direction required by Mohr–Coulomb’s associative flow law. Pan’s principle is therefore demonstrated. This paper also presents the results of centrifuge model tests that show reasonable evidence to support Pan’s principle of maximum.