For the supercritical CO2 Brayton cycle of a sodium-cooled fast reactor, we carried out surface reaction tests for sodium temperatures ranging from 200 to 600°C. Based on the test results, we found that the reaction kinetics over the sodium temperature range of 300 to 550°C depends heavily on the temperature but is not sensitive to the velocity of CO2 flowing over the gas-liquid reacting interface explored in this study. Gaseous and nongaseous reaction products were sampled and analyzed quantitatively. The rates of the chemical reaction were determined by measuring the gas concentration of the CO/CO2 mixture. Then, we proposed a two-zone reaction model with a threshold temperature of 460°C. The kinetic parameters for each reaction zone were experimentally obtained.