Abstract: To investigate the mechanism for the photocatalytic degradation of coal-mine gas over self-made adsorption- type composite catalyst(15% Ga2 O3 / AC),the experiments of photo-assisted removing methane in simulated coal-mine gas are carried out. The compound effect,interfacial microstructure,pore volume,pore size distribution and specific surface area of composite catalysts are characterized by X-ray diffraction(XRD),high-resolution transmission electron microscopy(HRTEM) and low temperature N2 adsorption-desorption technique,respectively. The separation of photo- induced charge carriers,the transfer of photo-generated electrons and the generation of reactive species are studied by using photoluminescence spectrum(PLs) and electron spin resonance( ESR) spectra. Based on the analysis of meth- ane degradation kinetics,the effective photo-assisted degradation of low concentration coal-mine gas can be implemen- ted repeatedly,keeping almost unchanged removal efficiency. The introduction of coal-based AC can enhance the ad- sorption of methane,meanwhile improve the separation of photo-generated charge carriers,which contributes to producing more photo-hole(h+ ) and superoxide radical(O2·- ). The generated ·CH3 via CH4 hydrogen abstraction by h+ is further oxidized through the reaction with O2·- ,promoting the removal efficiency of methane. These results provide a theoretical basis for the gas control in the local region of coal mine using photo-oxidation technology.