Abstract: Classification of rock mass permeability structure types is the important content for geological exploration of water resources and hydropower engineering and evaluation of permeability. Based on the seepage controlling effects of rock mass structures, key factors that control permeability characteristics of rock mass are analyzed. They are lithology, faulted structure, weathering and unloading and karst effect. Principle of dividing rock mass permeability structure types are put forward. The anisotropic characteristics of rock mass is considered. According to the macroscopic permeability characteristics of rock mass, the permeability structures are classified into five types. They are discrete mass permeability structure, layered permeability structure, zonal permeability structure, netlike permeability structure and duct-like permeability structure. The classification method is applied to actual engineering cases. The classified results of permeability structure types of rock mass at the Xiaolangdi Project and the Three Gorges Project dam sites are present. The results show that reasonable identification of permeability structure types of rock mass is of the most significance for seepage control and drainage design of water resources and hydropower engineering.