Abstract: The method for calculating the random-fuzzy reliability in the limit equilibrium analysis of the stability of the steep slopes was given.The corresponding calculating formulas were deduced by combining fuzzy mathematics with the reliability theory.The random-fuzzy reliability of the slope engineering was expressed by the fuzzy(event)—exact(probability) index in the suggested method.Both of the objective attributes of the rock soil mass and the quantitative evaluation of the slope engineering stability were considered at the same time.The calculating formulas in the method are determinate and convenient for use.