In this paper, the dynamic behaviors of electrons in a small Penning ion source model are analyzed by Particle In Cell plus Monte Carlo Collision(PIC/MCC) particle simulation method combined with the Scalar Magnetic Potential finite-difference Method(SMPM). Mainly, the influence of magnetic shielding on the trajectory and spatial distribution of electrons in the discharge process is taken into consideration. The influence of magnetic shielding on the plasma impedance during the excitation discharge of Penning source is further discussed. The results show that the addition of magnetic shielding promotes the uniformity of both electron spatial distribution and radial velocity distribution in the source, which can be beneficial to the sufficient ionization of electrons and hydrogen background gas. Moreover, the plasma impedance stabilization zone II is extended by about 3 times compared with the previous one, which helps to enhance the source discharge stability and provide a reference for improving the source performance. In particle simulation, parallel algorithms are added to speed up particle simulation.