Abstract: Different from the commonly occurred deformation of reservoir bank, reservoir plate deformation together with valley deformation are new issues in engineering geology and directly threaten the safety of reservoir dams. Monitoring data shows that settlement or lift deformation has occurred during impoundment at multiple reservoirs that have been built. We take Xiluodu, Tongjiezi, Jiangya, Jinping and Xiaowan hydroelectric power stations as typical examples to investigate the geological causes of reservoir plate deformation from the perspective of regional hydrogeological condition variations. The findings reveal that topography, formation lithology, geologic structure and hydrogeological conditions are internal factors of reservoir plate and valley deformation. Besides, the reservoir level and impoundment processes are external factors triggering such deformation. External factors always act upon the internal ones. The reserch achievements will provide guidance for building physical models for under-construction and to-be-built hydroelectric projects and for accurately calculating, analyzing and predicting potential reservoir plate and valley deformation.