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Oxy-fuel combustion is one of potential technologies for carbon dioxide (CO₂) capture in fossil fuel fired power plants. Characterization of flue gas composition in the oxy-fuel combustion differs from that of conventional air-coal combustion, which results in the change of radiative heat transfer in combustion processes. This paper presents a numerical study of radiation intensity on lateral walls based on the experimental results of a 0.5MW combustion test facility (CTF). Differences in the oxy-coal combustion are analyzed, such as flue gas recycle, absorption coefficient and radiation intensity. The simulation results show that an effective O₂ concentration ([O₂]_effective) between 29 and 33vol% (equivalent to the flue gas recycle ratio of 72-69%) constitutes a reasonable range, within this range the behavior of oxy-coal combustion is similar to air-coal combustion. Compared with the air-coal combustion, the lower limit (29vol%) of this range results in a similar radiative heat flux at the region closed to the burner, but a lower radiative heat flux in the downstream region of the CTF; the upper limit (33vol%) of this range results in a higher radiative heat flux at the region closed to the burner, while a similar radiative heat flux in the downstream region of the CTF