Abstract: The thermal behavior of maceral particles was investigated using the micro heating stage. The phenomena of devolatilization and semicoke contraction on pyrolysis of the particles were observed directly in the micro-picture taken online. The curve of the particle area which changed with increasing the temperature was obtained by means of image analysis on the micro-picture. The results of the above processes showed that three stages were involved in the process of semicoke contraction: slow contraction stage, transitional contraction stage, and rapid contraction stage. The values of the apparent activation energy, pre-exponential factor, and reaction rate constant might increase in the three stages as a result of different features shown by the chemical bond breakage types, its bond energy as well as the free radical pieces, and condensation reaction in each stage. In terms of semicoke contraction, the reaction rate constant of vitrinite was bigger than that of inertinite; the reaction rate constants of ShenDong coal and its macerals with lower metamorphic grade were bigger than those of PingShuo coal and its corresponding macerals, namely, the former had better semicoke contraction reactivity.