Abstract: The primary fragment phenomenon of coal during combustion was introduced and one dimension model of single particle coal was established. The results indicate that the primary fragment of coal during combustion results from the accumulation of coal volatile, which leads to the production of pressure gradient in coal. This explains well the pulverization phenomenon of coal. The particle size distribution based on the primary fragment inside the combustion chamber could be predicted in the future. In the meantime, the effect of primary fragment of coal on design and operation of circulating fluidized bed combustion boiler was also demonstrated.