Abstract: The CFD–DEM coupled with heat transfer and chemical reaction sub-models was developed for modeling the oxy-char combustion in a fluidized bed. After validating the model, the char thermal conversion characteristics including the reaction rate, the combustion temperature, and the heat transfer flux and contribution were investigated under various combustion atmospheres, fluidizing velocities, and char properties. Results reveal that the higher temperature of the char floating on the bed surface is induced primarily by the decreasing convection heat transfer. The convection heat and the radiation heat contribute more than 90% to preheat the char particle, with the convection heat being the most significant. The reaction heat contributes approximately 50% to the total heat transfer during the stable char combustion, with comparable contributions of the convection and the radiation found, but the higher char temperature associated with the increasing char combustion rates or the char floating behaviors will further increase the radiation heat contribution. On the other hand, the conduction heat plays an insignificant role regardless of the char combustion stage.