In this paper, molten blast furnace slag was used as a heat carrier to make the coal gasification reaction run smoothly. The characteristics of coal particle motion, heat transfer, and gasification reaction in molten slag were investigated in detail. It could be divided into four forms of coal particles in molten slag, and the coal particle could move across the bubble when the velocity and diameter of coal particle were 4.20 m s–1 and 75 μm, respectively. Meanwhile, with the coal particle motion, a large amount of waste heat of molten slag transferred it to ensure the process of the gasification reaction. The slag could enhance the heating rate of the coal particle, promote the gasification reaction, and increase the carbon conversion rate. Molten slag was also beneficial to the syngas production, which improved the fraction of CO and enhanced the combustible gas component in the process of coal/CO2 gasification. Moreover, the problem of sulfide emission in the coal gasification process was solved effectively using molten blast furnace slag as the heat carrier. The total sulfide emission decreased dramatically from 0.21 to 0.04 mol kgcoal –1. Overall, not only was waste heat of molten slag recovered by this method, but also the quality of coal gasification and reduced hazardous gas emissions improved.