Abstract: Oxy-fuel combustion is regarded as the most promising technology for large-scale carbon capture, which has been highly concerned in recent years. The changes of gas compositions under oxy-fuel conditions have great influence on the combustion process. In this paper, the effects of the physical and chemical properties of CO₂, O₂, and H₂O on oxy-fuel combustion were systematically studied, taking the non-premixed jet in hot co-flow system of methane combustion as a research object. The results show that the thermal, chemical, and diffusion properties of CO₂ can reduce the flame temperature. The increase of CO concentration is mainly caused by the chemical property of CO₂. However, the radiation effect of CO₂ on methane combustion is relatively weak. Furthermore, the increase of O₂ fraction can improve the flame temperature and the CO concentration while reduce the flame area, whether under air-combustion or oxy-combustion conditions. The increase of H₂O concentration decreases the flame area, which is more obvious at low O₂ concentration. The increase of H₂O concentration can reduce the CO concentration. And under O₂/CO₂ conditions, the reduction of CO is more significant when the O₂ concentration is higher.