A model study of the rheological behavior of the coal melt is proposed. Effects of intragranular heat and mass transfer, particle size, porosity, deformation of viscous melt, etc., are considered, so as to explain the striking phenomena of swelling and shrinking deformations for a single particle at various heating rates. This model gives both qualitative and quantative descriptions of the transient swelling characteristics, particularly the ’’cenosphere’’ formation during the pyrolysis of bituminous coal. The theoretical predictions show reasonable agreement with the experimental observations of microscopic studies.