By investigating the space development rule of the epigenetic deformation and fracture trace and the combination pattern of epigenetic structure in dam area of Xiluodu hydropower station, the formation mechanism of epigenetic reformation is discussed in conjunction with the analysis of geologic physiological evolvement mechanism. Slaty rock mass structures which being made up of flat faults have played important role in controlling epigenetic reformation. The typical combination pattern of epigenetic structure is formed from steep dipping and flat faults. It is very important for understanding the feature of valley rockmass structure.