The research about seepage of RSA is little, but the material is familiar. There are many difficulties in laboratory research about the materials, so numerical simulation research in the paper is introduced. The model of the random structure about SRA is set up, and then the study of seepage is given. The conversion of the two boundaries is solved correctly in the computer program. So some conclusions are drawn that the rock blocks the seepage to some degree, and the changing of RSA seepage is little under the effect of the fluctuating of rainfall intensity, namely the changing of the seepage is less than the fluctuating of rainfall intensity. The study is the foundation of the next study about the coupled of stress and seepage of RSA.