Underground coal gasification (UCG) technology can directly convert coal resources to syngas underground, making it important for coal utilization. In this work, the power generation, CO2 electrolysis, and reversible operation of flat-tube solid oxide cells (SOCs) fueled with UCG syngas were studied. The factors affecting the performances of flat-tube solid oxide cells were investigated. Fueled with syngas (Swan Hills, Canada) at 750 °C, the flat-tube cell achieved a maximum power density of 329.4 mW cm−2 and a current density of 650.8 mA cm−2 at 1.4 V. 100-cycle (250 h) reversible operation of flat-tube SOCs running on syngas (Swan Hills) was accomplished. No carbon deposition on the surfaces of the cell fuel channels was detected. The syngas conversion in flat-tube cells was illuminated based on density functional theory calculations.