Abstract: The coalification of sapropelic coals have been not understand very well. In this paper, the authors, basing on the sapropelic coals occurring in China with different ranks and geological times, combining the resules of the thermal simulating tests, investigate, the characteristics of coalification of sapropelic coals during coalificatoin including the changes of macro-and micro-petrological characteristics, elements composition and chemical structure through comparing these resules with humic coals. On the basis of this, the coalification mechanism of sapropelic coals is discussed, its rank parameters are studies and a rank classification suggested.