Abstract In the oxy-coal combustion steam system (OCCSS), the demineralized coal is consumed by reacting with O2 and steam. The stability and efficiency of demineralized coal combustion at high steam concentrations could be a critical issue to the development of mature OCCSS technology. In this study, Zhundong coal and its acid-washed sample were used for conducting experiments. Pyrolysis chars were firstly prepared from the raw coal and the demineralized coal in a high-temperature drop tube furnace at 1200 °C. The effects of the reaction atmosphere (O2/steam and O2/N2) and temperature (1100–1400 °C) on the combustion characteristics of the two char samples were then investigated. The results show that compared to the char from pyrolysis of raw coal, the char from demineralized coal contained abundant macropores with low specific surface area. For the pyrolysis char from demineralized coal at 1200 °C, the steam-char gasification reaction rate was significantly lower than that of O2-char reaction. The presence of high concentration of steam could alter the heat/mass transfer on the char surface, thus indirectly reducing the rate of O2-char reactions. The combustion of char without minerals in an O2/steam atmosphere accelerated significantly with increasing temperature, while the increase in combustion rate with increasing reaction temperature for char containing minerals was very limited. The steam-char gasification reaction of demineralized char at 1300 °C has promoted the carbon conversion of char. The demineralized char combustion reaction required a relatively high oxygen concentration (i.e. above 40%) to show high burning rate.