The H2O concentration in real oxy-fuel combustion atmospheres is significantly higher than that in conventional air combustion, which strongly affects the combustion characteristics of pulverized coal. This study studies the effect of H2O on pulverized coal combustion behaviour in O-2/CO2 atmosphere. The ignition temperature, burnout temperature and comprehensive reactivity of three types of Chinese coal at different H2O and O-2 concentrations in O-2/CO2/H2O atmosphere were investigated. The effect of particle size and heating rate on the pulverized coal combustion was also studied under high-H2O-concentration oxy-fuel atmosphere. The results showed that the presence of H2O strongly affects the combustion characteristics of coal and coal char in O2/CO2 atmosphere, leading to a greater ignition delay, faster burnout and higher comprehensive reactivity. These changes are more obvious for brown coal. Under O-2/CO2/H2O atmosphere, H2O can improve the diffusivity and heat capacity of the combustion atmosphere and therefore has a positive effect on pulverized coal combustion. In addition, based on a comparison of the combustion reactivity between O-2/CO2 atmosphere with and without H2O, the mechanism of coal combustion reactivity in H2O-containing atmosphere is significantly related to the heating rate. (C) 2014 Elsevier Ltd. All rights reserved.