Molten ash slagging moving bed gasification technology is significant for lump coal utilization. Mathematical modeling is essential for a comprehensive understanding of transport and reaction phenomena in a gasifier. In this work, a model based on the impact of bed characteristics was proposed, encompassing: (i) particle fragmentation and agglomeration varied the particle size and bed voidage, (ii) gas channeling weakened the gas-solid heat transfer efficiency and variation of the gas phase temperature, and (iii) molten ash covering coal surface attenuated the gas-solid reaction rate. A good agreement was found between the simulation results of the proposed model and industrial data. Finally, the effects of the operating and model parameters were studied. The results indicated that the steam flow rate had a significant influence on the product gas composition, and the temperatures of gas and solid phases were sensitive to the gas channeling factor.