Steam is the main byproduct of flue gas recirculation in the oxy-coal combustion system. Coal particles are commonly surrounded and burned under the steam-rich atmosphere. In terms of the distinct physical and chemical properties of steam, the high-concentration steam would substantially affect the oxy-coal flame by changing the heat capacity, radiation and gasification. This work aims to numerically investigate how these properties affect the oxy-coal flame under a steam-rich atmosphere at a pilot-scale furnace. The results show that the flame temperature is controlled by both the heat capacity and radiation and is dependent on the oxygen and steam volume concentration. Char consumption by the steam-char gasification reaction increases as the steam volume concentration increases. In turn, char consumption by the oxidation reaction decreases. The temperature gradient in the in-flame region gradually decreases as the steam volume concentration increase due to the enhancement of the gasification reactions. Under steam-rich atmosphere, the occurrence of the steam-char gasification occurs much earlier than the CO2-char gasification. Increasing the oxygen volume concentration can lead to an incremental increase in char burnout time due to the enhancement of the gasification reactions under steam-rich atmosphere. (C) 2015 Elsevier Ltd. All rights reserved.