The conversion mechanism between CH4 and CO2, two essential volatiles in earth system, is one of the most important scientific problems that is significantly related to many geological processes, such as carbon cycle and fluid- rock interaction. For example, CH4 and CO2 have a deep impact on the migration and enrichment of ore- forming elements, since CH4 and CO2 could change the properties of ore- forming fluids in the process of mineralization, especially CO2 could buffer the pH of fluids. Based on the fluid inclusions in fractured quartz from Carboniferous, Permian, and Triassic strata in central Swiss Alps, it has been shown that CH4 might be oxidized to CO2 along with the chloritization of biotite at high temperatures. However, there is no relevant experimental work to illustrate it. This study focused on the oxidation mechanism of methane through a series of laboratory experiments using biotite as the oxidant. Through three batches of experiments ie, (1) biotite, methane and water, (2) biotite, aluminum carbide and water, (3) methane and water, this study confirms that CH4 can be oxidized to CO2 by biotite at an initial reaction temperature of ~150℃, which is much lower than the results of field geological studies. Fused Silica Capillary Capsule was used for batch one and three, and thick quartz tube was used for batch two. The energy spectrum analysis on residual biotite show that the content of Fe in biotite decreases greatly, indicating that the trivalent Fe in biotite was involved in the reaction as an oxidant. This result provides experimental and theoretical support for the oxidation of CH4 to CO2 by biotite and other Fe- Mn minerals in geological system at low temperature. The conversion of CH4 to CO2 will change the properties of hydrothermal fluids, which could benefit the formation of CO2- rich ore- forming fluids, and is significant for the formation of metal deposits.