In this study, a spectral measurement method of key characteristic parameters, such as plasma density and electron temperature, is proposed for the ion extraction simulation study, which produces plasma through argon discharging. According to the argon plasma state, a particle population equilibrium model of kinetic reaction processes among the main particles is established. By comparing and analyzing emission spectra acquired in the experiment, information on corresponding plasma characteristic parameters can be obtained. The experimental results show that under the typical working conditions, the proposed spectral measurement method is used to obtain key parameters such as the density and electron temperature of the argon plasma in the jet region, thereby providing a reliable and practical measurement method for the simulation studies on the ion extraction process.