Coalbed stimulation is a process of increasing coalbed methane (CBM) production by opening, enlarging, and extending the length, width, and connectivity of pores and fractures/cleats. Microwave irradiation is a promising thermal stimulation technique for coal reservoirs. To investigate the effects of microwave heating on the methane adsorption capacity of Pingdingshan bituminous coal, molecular models were constructed based on proximate analysis, ultimate analysis, solid-state 13C nuclear magnetic resonance (13C-NMR), and X-ray photoelectron spectroscopy (XPS). The results show that the condensation degree of the aromatic ring in Pingdingshan coal is 0.18, and the molecular formula is C143H153N3O5. Microwave irradiation causes the cracking of aromatic hydrocarbons, and the molecular formula of coal evolves into C132H133N3O4. After microwave irradiation, the saturated adsorption number of CH4 molecule decreases from 12 to 7, indicating that microwave heating can promote methane to diffuse from the coal matrix. Carboxyl and pyrrole are not favorable for methane adsorption. Microwave irradiation has the weakest effect on carbonyl. This study contributes to understanding the effect of microwave heating on CH4 adsorption mechanism of coal from the molecular perspective.