Abstract: The relationship between the raw coal ash content and the structural differentiation was studied by using statistics and the principles of dissipation structures. Shear repture of a seam might be divided into three phases, i. e. breaking, granulation and pulverization. Compared with the ash content of the original tectonic coal, the raw coal ash content of the three phases were respectively equal, increased and decreased. Those regular changes of raw coal ash content were related to the structural differetiation. In fact, the differentiation of coal by structures was an irreversible process of tectonic coal from a disorder status du ring the granulation phase to a new order status after recombination of coal and non coal components during the pulverization phase.