Abstract: Low temperature plasma technology is an effective means to achieve carbon sequestration and emission reduction of methane. However, the research on coal bed methane has not yet been carried out in-depth. To explore the influencing factors and action rules of transformation of coal bed methane by low-temperature plasma, the CH_4-N_2-O_2-H_2O experimental system was constructed with corundum as discharge medium, threaded stainless steel rod as high pressure electrode, wire mesh as low pressure electrode. The influence of input voltage, discharge frequency, methane volume percentage on transformation of methane and product formation were investigated under the conditions of a 1 mm discharge gap and a discharge area of 200 mm in length. And based on the in situ diagnosis of the emission spectra of the active species during the reaction, the pathways of the main products were analyzed. The results show that the main products are hydrogen, carbon monoxide, carbon dioxide, methanol, ethylene, ethane and other C_2 hydrocarbons. The methane transformation and product formation are affected by the input voltage, discharge frequency and CH_4 volume fraction, because the input voltage changes the injection energy and energy loss of DBD system, discharge frequency changes the amount of streamer discharge in the reactor and volume percentage of methane changes the oxidation environment. In the range of experimental research, the optimal conditions are input voltage 75 V,discharge frequency 9.8 kHz; the optimal volume percentage of methane is 35.4% when the yield of methanol is used as the index. Active particles such as CH_3·,CH_2·,CH·,C·,O·,OH·,H_γ,H_β,H_2 and H_α are generated during plasma reaction. These active particles interact with steady-state molecules and interact with each other to form product molecules. The results are of great significance to further study the process conditions and reaction mechanism of low-temperature plasma activation coal bed methane.