The contact metamorphic coal, the recorder and carrier of coal seam engulfed by magma, is an important research object to reveal the rapid thermal carbonization process and mechanism of coal. Samples of the contact metamorphic coal with different thermal metamorphic degrees in the Shitai coal mine, North China were collected to reveal ultra- microfabrics characteristics, mechanism and process of rapid thermal carbonization of coal by means of vitrinite reflectance test, proximate analysis, ultimate analysis, polarized light microscope (PLM) and scanning electron microscope (SEM) in this study. The results show that the vitrinite reflectance and ash contents increase, while the H, N and volatile matters decrease from the unaffected coal, the slightly metamorphosed coal to the natural cokes. The unaffected coal is mainly composed of collotelinites with a bit of fusinites. There are many fractures and few devolatilization pores in slightly metamorphic coal. Mosaic carbons and devolatilization pores are developed in the massive natural coke near the sill, and the pore diameters are 20~150 μm. Fine veined natural cokes in the sill, mainly composed of porous carbon and mesocarbon microbeads (MCMBs), are rich in round and oval pores, and the pore diameters are mostly between 1~3 μm. The analysis shows that the thermal metamorphism degree of contact metamorphic coal increases continuously approaching the sill. The slightly thermal metamorphic coals are the result of brittle fracture of unaffected coal due to weak thermal metamorphism. Natural cokes are the products of devolatilization and mesophaseization during pyrolysis of slightly metamorphic coal. Near the sill, the natural cokes are liquefied into porous carbon and MCMBs, which are finally oxidized into gaseous carbon oxides and disappear. We believe that the essence of carbonization of magma contact metamorphic coal are mesophaseization, liquefaction, oxidation and gasification of solid coal.