This study analyzes the causes and forming conditions of valley deformation based on the geological environment of Xiluodu hydropower station and the evolution of regional hydrogeological conditions induced by the impoundment. It reveals that the foundation and valley deformation are related to facts that the dam is located within the Yongsheng synclinal basin and the basalt layer consisting of the dam foundation situates above a thick confined aquifer consisting of Yangxin limestone. The patterns of valley and foundation deformation are closely related to the regional geological conditions, hydrogeological conditions and the reservoir impoundment process, etc. On such basis, internal and external factors of foundation and valley deformation are revealed. At the same time, it has been pointed out that the foundation and valley deformation belong to a special bank deformation. At last, definitions and classification of two deformation types are provided.