In order to explore key technologies to improve the combustion of agricultural internal combustion engine, characteristics and influencing factors of methane plasma in the coaxial dielectric barrier discharge process are analyzed. A two-dimensional axisymmetric actuator model is established, and the discharge process is numerically simulated by finite element method. The changes of electron density, electron temperature, CH₃ and H number density under different voltage amplitudes and different dielectric materials are analyzed. The simulation results show that voltage amplitude affects the change of current, and the change of electron density and electron temperature are affected by the current. When the input voltage changes, the energy of ionized methane changes with the voltage, and when the voltage amplitude increases, the electron density and electron temperature increase. When the energy consumed by the collision between particles is greater than the energy released by ionization, Electron density and temperature decreased; The number density of CH₃ and H increases with time, and the higher the voltage amplitude, the faster the growth rate. The electron density and the electron temperature increase with the increase of the relative dielectric constant, and the number density of CH₃ and H increases with the increase of the relative dielectric constant. Increasing voltage amplitude and relative dielectric constant will further intensify the ionization of methane.