The sheet beam klystron (SBK) is characterized by a large rectangular drift tube, which allows the use of a high current, low voltage beam, resulting in a low beam current density, and hence high efficiency and the possibility of Periodic Permanent Magnet (PPM) focusing. Our research group has designed a 5-Cavity X-Band SBK recently. In this paper, we discusses the general design of this X-Band SBK and presents the transfer characteristic of it predicted by a large signal code we developed.