Abstract:A self-consistent two-dimensional fluid plasma model coupled with Maxwell's equation at medium pressure is established, and a series of kinetic reaction equations of molecular ions are also added. We demonstrate the changes of electron density, temperature, electric field module, skin depth and other parameters in the excitation process at medium pressure. The dominated reason for the spatial distribution of molecular ions is analyzed. In addition, compared with the atmospheric pressure microwave plasma, it is found that the gas temperature of the medium pressure microwave plasma is lower and the damage to the glass tube is smaller. It can be applied to the treatment of various exhaust gases, the synthesis of nanoparticles and the preparation of thin films, which is easy to achieve large-scale, and has a good application prospect.