High-purity Na2SnO3 product has been successfully prepared from SnO2 and Na2CO3 via a novel process developed by the authors' group. This study proposed a function mechanism of CO-CO2 atmosphere on the formation of Na2SnO3 in the roasting process using SEM-EDS, micro-region XRD and FTIR analyses. The results showed that under 5 vol%-20 vol% CO/(CO + CO2) atmosphere, the main reactions in the SnO2-Na2CO3 system included Na2CO3 = Na2O + CO2 and Na2O + SnO2 = Na2SnO3. The reactions were affected by the CO2 partial pressure as well as by the CO content in the CO-CO2 atmosphere. The formation degree of Na2SnO3 increased with the decrease of CO2 partial pressure. When the CO content varied in the range of 5 vol%-20 vol%, the formation degree of Na2SnO3 was promoted. There was a lot of bridging oxygen (SnO2 center dot center dot center dot O-) on the SnO2 surface, while in the roasting process, the CO gas molecules were firstly adsorbed on the SnO2 surface and then combined with the bridging oxygen so that some oxygen vacancies were formed, and the reaction was expressed' as SnO2 center dot center dot center dot O- + CO = SnO2 + CO2 + e. These vacancies were replenished by the active oxygen anions coming from the Na2O. This process accelerated the formation of Na2SnO3. (C) 2016 Elsevier B.V. All rights reserved.