A new method for optimizing ultra-fine pulverization and abating reactive condition of coal liquefaction is investigated. The single fractal and multifractal approaches are applied to analyze the fractal size dimensions of coal samples at various points within 25 h during the ultra-fine pulverizing process. Pyrolysis and infrared spectrum analyses of the samples are carried out and first expressed with the fractal size dimension of smaller particles by a bi-fractal law. It is shown that the fractal size dimension values of smaller particles are ranged from 1.715 to 1.909 and the minimum is 1.715 at 7 h. The breaking of partial chemical bonds and high pyrolysis reactivity have been demonstrated. Finally, the fractal size dimension is proposed as a promising parameter of the combined reactor of both coal ultrafine pulverization and liquefaction.