The solid oxide fuel cell (SOFC) is expected to be a candidate for distributed power sources in the next generation due to its high efficiency and high-temperature waste heat utilization. In this study, the 5-cell SOFC stack was operated with pure hydrogen or reformed gas at anode side and air at cathode side. When a stack was operated with diesel and methane ATR reformer, the influence of the $H_2O/C$, $O_2/C$ and GHSV on performance of stacks was investigated. The result shows that the cell voltage was decreased with the increase of $H_2O/C$ and $O_2/C$ due to partial pressure of fuel and steam, and cell voltage was more sensitive to $O_2/C$ than $H_2O/C$. Next, the dynamic model of SOFC system included with ATR reformer was established and compared with experimental data. Based on dynamic model, control strategy to optimize SOFC-Reformer system was suggested and simulated. Finally, a commercial software package, STAR-CD, was utilized to simulate distribution of temperature, CO, and $CO_2$ in single cell as inlet condition. These results could be used as guideline for development of 1kW RPG system.