[en] Technical review of conceptual multi power conversion system with productions of electrical power and hydrogen synthesis gas by methane partial oxidation reaction in combination of gas cooled reactor and SOFC was made. This system can produce electrical power, hydrogen synthesis gas and power load by coupling HTGR to supply high temperature thermal energy to cover enthalpy change in the methane reforming process. In present paper the performance of this system was discussed, and the following conclusions were derived. (1) This system requires very high performance electrolyte materials for SOFC in the high temperature service over 1,000 K, and CeSmO₂ materials was doped by 3b elements such as Al³⁺, Ga³⁺ and Ga³⁺, and it is found that In³⁺ dopant improves density and ion conductivity of CeSmO₂, and best composition of the doped material was optimized as Ce_0.8Sm_0.15In_0.05O_1.9. (2) In the methane partial oxidation test with SOFC single cell of Ce_0.8Sm_0.15In_0.05O_1.9, 74% free energy change was converted into electrical power and 90% methane reforming was achieved. (author)