This paper aims to convert NaHCO3 (dissolved carbon dioxide in NaOH solution) into methane via hydrothermal catalytic reaction. The effects of various experimental parameters on the conversion efficiency of NaHCO 3, e.g., amount of reactant (Zn) and catalyst (Ni), temperature, reaction time etc, were investigated. The results showed that a maximal 43.6% yield of methane was obtained at the optimal conditions: Zn 0.1mol, Ni 0.06 mol, temperature of 300°C, reaction time of 120min, filling rate of 35% and NaHCO3 0.01mol. In the absence of Ni catalyst, CO2 was mostly converted into formic acid (formic acid yield of 87%) and the corresponding methane yield was zero, while in the presence of Ni, the yield of methane increased to 43.6% and the yield of formic acid was only 3%. Based on these results, it was supposed that Ni played a catalytic role in hydrothermal conversion of CO2 into methane and formic acid was the intermediate product during the formation of methane from CO2 in the hydrothermal processes.