A macro-homogeneous model has been developed to evaluate the impact of replacing conventional flooded electrode with gas diffusion electrode on the performance of a novel non-aqueous Na-air battery under pure oxygen gas. After the model has been validated with experimental data, the model results exhibit a significant improvement in battery performance, providing about a 48% increase in initial discharge capacity (over 1551 mAh/gcarbon at 0.1mA/cm2) and higher discharge potential when using a gas diffusion electrode rather than a flooded electrode. Overall, the gas diffusion electrode model shows the promising performances for a rechargeable Na-air. The model correlates the relationship between the performance and electrolyte decomposition and the formation of discharge products (such as Na2O2 and Na2CO3). The developed model can be potentially used to optimise electrode structure and electrolyte loading in the active layer, leading to improve the battery performance.