Abstract: Based on the theory of limit analysis,a new approach to evaluate the slope stability based on a factor of safety defined in terms of energy ratio was proposed.Examples were presented to show the details of this approach.It was shown that the energy-based safety factor had a clear physical meaning for designing the two dimensional slope,and was easy to be applied to determine the local pressure on top surface of slope under complicated three-dimensional boundary conditions.Finally,it was pointed out that the present two three-dimensional failure mechanism was reasonable and appropriate to be used as an engineering tool for slope stability analyses.