The seepage stability and the role of the transition zone material to control seepage field is very important for the super high concrete faced rockfill dam (CFRD) of Shuibuya Hydropower Station. The study process of its design requirements was reviewed. With big seepage test apparatuses and water supply system set up specifically for this project, seepage deformation tests were performed for the first time on the whole size gradation curves of the transition material. The test results were compared with the design requirements and the expected situation of the seepage field in the dam. The lower limit of the material permeability coincides with the design, and the upper one would exceed the design with one magnitude. So the transition zone will drain more quickly than design. Under the normal condition that the concrete face functions well, the seepage stability of the transition zone will be satisfied. While the concrete face cracks locally or does not work totally and reservoir water level remains at design water level, fine grains would be driven out from the transition zone. Then the interior structure of the material would be unstable, but the framework of the transition zone would remain stable with the support of the main rockfill zone.