The dam body and foundation seepage is one of the important points in design parameters. This index is related to the permeability. Therefore permeability is one of the basic parameter in design grout curtain, prevent water escape from foundation and avoid negative seepage pressure in borrow materials, so grouting is used. Jamishan rockfill dam with clay core is located in northeast of Kermanshah on the Jamishan River that is one of the branches Karkheh river. The dam foundation located on the schist conglomerate and schist limestone. The main aim of this study is determination of permeability dam site based on calculation hydraulic aperture of joint, secondary permeability index (SPI) and lugeon value. The permeability of dam site cannot estimate alone with Rock Quality Designation (RQD) and lugeon values because in the zones with similar lugeon value may frequency and aperture of joint is deferent. So, frequency and aperture of joint was calculated and analysed in dam site. Type of cement for grouting operation, grouting pressure and grouting curtain was designed and recommended with considering this data.