Abstract: Based on the analytic expression of the ion trajectory in the radial electric field, the ion focusing trajectories of ions with the characteristic mass in the radial electric field were simulated by using MATLAB. The results show that the ions with different masses in the radial electric field are focused according to their masses, and separation can be seen obviously from the locus. This study can lay a theoretical foundation for the development of the plasma optical mass separator device. Furthermore, it has a certain value of reference for the special-shaped electromagnetic field control of plasma technology.