A one-dimensional fluid model has been used to describe the effect of radio frequency (RF) on the characteristics of carbon dioxide (CO2), nitrogen (N2) and helium (He) mixture discharge at 120 mbar in fast-axial- flow RF-excited CO2 laser. A finite difference method was applied to solve the one-dimensional fluid model. The simulation results show that the spatial distributions of electron density and current density rely strongly on the modulating driven frequency. When the excitation fre- quency changes from 5 to 45 MHz, the plasma discharge is always in a mode. Moreover, as the excitation frequency increasing, the higher densities of COv and N2vib can be obtained, which is important to get higher excitation efficiency for the upper laser level.