Abstract: In the context of dual-carbon resources, in order to achieve efficient and clean utilization of coal, an improved layer combustion method coupled with fluidized fine coal particles is adopted to enhance the combustion efficiency of coarse coal in grate furnace. Experiments are conducted to provide theoretical explanations for this phenomenon. Firstly, the feasibility of the composite combustion method was confirmed by isothermal combustion experiments within the tube furnace. Combustion characteristics are compared between cases of mixed fine/coarse coal and single coarse coal particle, in terms of flue gas composition, particle surface temperature, ignition time, and burn-out time. Both gas phase and solid phase data were analyzed to verify the combustion-promoting effect of fluidized fine coal. In addition, the influence of bed temperature, proportion of fine coal, and air flow on the combustion of mixed fine and coarse coal was systematically studied, with a focus on ignition time, burnout time, carbon conversion rate, particle surface temperature, and reaction index. This provides theoretical guidance for the practical application of the composite combustion method in layer combustion furnaces. To gain a deeper insight, an isoconversion method was used to analyze the combustion of mixed fine and coarse coal. The data indicate that, in the presence of fluidized fine coal, the ignition time is advanced by 59%, the burnout time is shortened by 26%, and the solid weight loss ratio is up to 98% within 6 minutes, demonstrating excellent ignition and combustion promotion effects. Factorial experiments show that the burning fluidized fine coal creates a high-temperature zone around the coarse coal. When the coarse and fine coals are mixed and burned, they can be ignited quickly at lower temperature （550 °C）. The optimized fine coal proportion is 33%. Furthermore, increasing the air flowrate can lead to early ignition and significantly shorten the burn-out time, but higher wind speeds will bring about convective cooling. Finally, kinetic calculations give an average apparent activation energy of 26.37 kJ/mol.