In this paper, an innovative natural uranium-thorium fuel fusion-fission hybrid reactor (FFHR) design aiming at closed thorium-uranium fuel cycle, and which could operate with high energy gain, fast 233U breeding rate and tritium self-sufficiency, is presented. The reactor consists of two main modules, i.e. natural uranium module and thorium module, which are placed alternately in the blanket’s toroidal direction. Uranium module plays the role of energy generation and neutron multiplication at the initial stage. Excess neutrons are then used to drive the thorium module to breed 233U. After the 233U inventory reaches a certain level, the uranium module is then replaced by new thorium fuel module. The system is transition to the all thorium fueled operating mode. With appropriately selected thorium fuel to water volumetric ratio, the system could then be started by the limited bred 233U. The blanket could reach thorium-uranium closed fuel cycle with high energy gain and tritium self-sufficiency. The system could burn up about 90 tonnes 232Th at the end of 60 years operating.