Solid oxide fuel cells (SOFCs) have been studied as power generation systems because of their high efficiency and power density. In addition, due to the high operating temperature and the flexibility of the fuel due to the metal catalyst of the fuel electrode, natural gas can be used directly as fuel. Methane, which is predominantly in natural gas, is used as fuel through thermochemical reactions such as methane reforming reactions and water gas conversion reactions inside hot SOFCs. Therefore, methane operation is essential to take advantage of SOFC. In this study, the difference between hydrogen operation and methane operation was compared using a 3D SOFC model with high fidelity.