Abstract: When the set pair analysis is applied to evaluate slope stability, the connection degree is usually decided by linear function, which can't reflect the actual conditions of the engineering project objectively and comprehensively and neglect the system randomness. The set pair analysis theory is improved by application of cloud theory which is superior in dealing with the connection degree and set pair analysis-cloud model of slope stability evaluation is established. In this model, the weight matrix is obtained by using the cloud theory to improve the AHP, and the evaluation matrix is obtained by combining with the connection degree evaluation matrix. Then the cloud model of the result of slope stability is generated, in turn the evaluation results and their visual cloud figures are obtained. The X-cloud generator can be used to calculate the probability of different grades. The model was applied in slope engineering, comparative analysis was carried out for the existing models and engineering practice to verify the veracity of the model, and the stability of different slopes was ranked. The model combines the advantages of the cloud theory and set pair analysis, considers fully the randomness of the system, provides a scientific and accurate method for the slope stability evaluation.