Abstract: This study focused on the dam foundation rock quality evaluation. Six evaluation indicators involving saturated uniaxial compressive strength， structural plane spacing， RQD， integrality coefficient， acoustic longitudinal wave velocity and ground stress correction coefficient were taken into consideration. Based on the component weighting method and cloud model， the Jinsha Xulong dam foundation rock mass was taken as a case. The optimal sequence diagram method and entropy value method were combined by the preference coefficient method to overcome the disadvantages of using subjective and objective weighting method alone. The rock mass quality evaluation indicators clouds were established based on the digital characteristic values. Then the certainty of each indicator was calculated. The corresponding quality degree is the rock mass quality degree. The cloud model results were compared with traditional BQ method results and the extension theory results. The cloud model has stronger controllability and higher classification accuracy， which is able to express the comprehensive uncertainty of rock quality.

Key words: cloud model, rock mass quality evaluation, component weighting method, comprehensive certainty