Abstract: Plasma-facing materials, which act as the primary interface between fusion plasma and nuclear reactor structures, are subject to harsh irradiation conditions. To improve the research of plasma-facing materials, the laboratory simulation fusion environment device is of great significance. Based on the completed ECR linear plasma device for studying the interaction between medium ions and materials in fusion reactors, the distribution of the superimposed magnetic field of the excitation coil and the permanent magnet in the chamber and the trajectory of charged particles in the magnetic field under this background magnetic field were calculated and simulated by finite element method. Results show that the magnetic field simulation results are more consistent with the experimental data, and the position of the resonant surface is far away from the microwave window with the increase of the coil current. The simulation results of the charged particle locus are consistent with the distribution of the approximately "pear-shaped" plasma beams in the experiment, and the beam density reaching the sample stage increases with the increase of the excitation coil current. This result can provide a reference for further optimization of the ECR linear plasma device.