Abstract: Coalbed gas bioengineering technology is one of the effective means to achieve a green and low-carbon development of tar-rich coal. To explore the pore structure evolution characteristics of tar-rich coal during the process of biodegradation, tar-rich coal samples from the Huangling mining area in the southern Ordos Basin were investigated. The simulation experiment of anaerobic fermentation or biodegradation of coal and hydrocarbon generation was carried out under laboratory conditions. The surface morphology, roughness, and internal pore space of tar-rich coal before-and after-biodegradation were characterized utilizing field emission scanning electron microscopy(FE-SEM),three-dimensional(3D)morphometry, computer tomography(CT)scanning, and porosity/permeability test. The evolution law of tar-rich coal reservoir pore structure under biodegradation and the enlightenment of geological development were also discussed. The results show that the methane yield with different sizes is positively correlated with the coal quality or contact area between microbe and coal. Biodegradation has some significant effects on pore expansion, pore increase, volume increase, and fracture formation, as well as reducing the surface roughness of the coal body and making it smooth, which is beneficial to the desorption and transport of coalbed methane. Microorganisms can also enter the interior of tar-rich coal along the joints and fracture system to modify the pore structure of the coal body and its connectivity. At the same time, biodegradation can also increase the porosity and permeability of tar-rich coal reservoirs, providing a good channel for coalbed methane seepage and transport. Microorganisms mainly act on the branched chains on the aliphatic groups in the coal to break the weakly connected hydrogen bonds between small molecules, reduce the degree of branching of the aliphatic groups and the degree of cross-linking of the coal structure, and then produce methane. Biodegradation can also break the bonds connected between the aromatic layers of tar-rich coals, increase the web spacing, change the aromaticity and the degree of condensation of aromatic rings, and thus change the molecular and pore structures of coal. The difference in methane generation mechanism between tar-rich coal and non-tar-rich coal in microbial anaerobic fermentation is worthy of further study.