High temperature electrolytic water vapor technology based on solid oxide electrolytic cell is a technology that can realize large-scale hydrogen production under low carbon emission conditions. The working conditions of solid oxide electrolytic cell, especially the composition and pressure of the gas introduced, have great influence on its performance. Based on computational fluid dynamics (CFD) software, the theoretical model of electrolytic cell was established, and the influence of purge gas with different oxygen partial pressure on the reaction characteristics of solid oxide electrolytic cell was studied. The range of oxygen partial pressure studied in this paper is1.01×103-1.0×105 Pa. The results show that the reversible open circuit voltage increases with the increase of oxygen partial pressure. The polarization voltage caused by activation polarization, ohmic polarization and concentration polarization decreases with the increase of oxygen partial pressure. At low current density, the smaller the oxygen partial pressure, the better the performance of the solid oxide electrolytic cell, while at high current density, the higher the oxygen partial pressure, the better the performance of the solid oxide electrolytic cell. Therefore, using low oxygen partial pressure purge gas at low current density is beneficial to reduce the power consumption of electrolytic water, and using oxygen as purge gas at high current density can improve economic value.