Abstract: Based on the discussion of combined indices, which reflect the factors influencing rock slope stability,such as rock quality, structural faces of rock masses and slope geometry properties, the effectiveness of employing the gray correlation method to estimate the rock slope stability is validated through examples. The results show that the gray correlation analysis method can provide quantitative measures to geological-engineering analogy and it is practical and feasible to apply the five combined indices and gray correlation analysis method to estimate the rock slope stability.