Abstract: Taking benches of slope in an open pit as the study object, Simplified Rosenblueth method as a new method of reliability analysis is presented and adopted to analyze the reliability of bench slope of primary design scheme and recommendatory scheme. The results indicate that high failure probability of benches is primarily depended on inherent variability of strength, anti-weathering ability and hydro-physical properties of moraine soil. And structure factors of slope bring little effects on it. The scheme of ternary benches whose platform widths are 3 m,3 m and 16 m is recommended and some effective measures such as holding up flood and revetment are put forward to enhance st,ability of benches.