The synthesis of oxalic acid by CO coupling reaction in gaseous phase is a circulating system with multi-step reactions. The best catalyst was prepared and the reaction mechanism was proposed in the past work. It was found that the key problem for scaling-up this process is to match the CO coupling reaction rate with the regeneration rate. In this thesis, these two reactions were simulated by analyzing the sensitivity of operating parameters based on the acquired reaction kinetics. It was proposed that the match of these two reactions is a complex non-linear process. The key technique was investigated during the scale-up experiments of catalyst preparation and CO coupling reaction. By analyzing the simulation and experimental results, the key problem for the match of CO coupling with regeneration reaction was resolved. The scale-up circulating system for oxalic production was continuously run for 1000 hours and no intermediates was vented. It was proved that the match of these two reactions was achieved and an environmentally benign process for oxalic acid production has been set-up after a series of study. It provides a new technology for industrial production of oxalic acid.