Changes in hydrogeological conditions directly affect the utility of water curtain systems and the safety of oil storage caverns during the construction and operation of underground water-sealed oil storage caverns. Therefore, hydrogeological conditions are of great importance in surrounding rock classification. This study is based on an actual project. The PCA-extenics model is applied to evaluate the exact hydrogeologic grade of the oil storage cavern. Then, the authors introduce rough set theory to calculate the weight of each influential factor. Finally, the research establishes the RS-extenics model for surrounding rock prediction based on the weights and evaluates the reliability of the model. The results suggest that the RQD has the most significant weight (0.3158) and is crucial to surrounding rock classification. The prediction results are generally consistent with the actual values. The results indicate that the model has good engineering applicability and value. The study provides a reference for the prediction of hydrogeological grades and classification of rock surrounding oil storage caverns.