Abstract: Effects of water vapor on the combustion characteristics of coal char were studied on the isothermal thermo-gravimetric measurement bench. The results show that under low oxygen concentration, water vapor affects the coal char combustion significantly, which noticeably increases the weight loss rate and reduces the burning time. Since the gasification reaction of water vapor and coal char happens and becomes weaker under the condition of more oxygen, the influence decreases with the increase of oxygen concentration.Moreover, the effects of water vapor on the combustion characteristics of coal char keep increasing with the rise of reaction temperature. Water vapor can improve the combustion characteristics of coal char even though carbon dioxide exists.Additionally, the effects of water vapor on the combustion characteristics of coal char reduce with coalification degree getting higher, in other words, water vapor can obviously affect combustion characteristics of the coal char with high reactivity.