A novel model of the solid oxide fuel cell-gas turbine hybrid system with fuel reforming is established, where the residual fuel from the fuel cell is further burned in a combustor and the solid oxide fuel cell (SOFC) and combustor act as the high-temperature reservoirs of the gas turbine (GT). The irreversibilities existing in real systems including the overpotentials and heat leakage in the SOFC, the finite-rate heat transfer between the working substance of the gas turbine and the reservoirs, and the irreversible compression, expansion, and regeneration processes in the gas turbine are considered. By using the theories of electrochemistry and non-equilibrium thermodynamics, expressions for the power output and efficiency of the hybrid system are derived and the advantages of the hybrid system compared with the pure SOFC are represented. The optimally operating regions of some of the important parameters including the power output and efficiency of the hybrid system and the rate of the fuel flowing into the SOFC are determined. The rate of the air flowing into the cell at the optimal efficiency of the hybrid system is also derived. The results obtained here may provide some theoretical bases and optimization criterion for the design and operation of practical syngas SOFC-based hybrid systems. (C) 2014 Elsevier Ltd. All rights reserved.