Abstract: The space-time evolution of moving electron beams is influenced directly by the distribution of the space charged particles, and the space radiation environment is an important issue. To simulate the space-time evolution of moving electron beams modulated by the Earth’s magnetic field, a self-consistent particle-in-cell (PIC) model is established by numerically solving the Poisson equation and the relativistic particle motion equation, along with the dipolar magnetic field model to represent the background field of the Earth’s inner magnetosphere (3≤L≤7). Based on these models, the kinetic process of the electron beams (0.1 keV≤E_k≤100 keV) travelling through the Earth’s magnetic field is simulated, for two different initial distributions (Uniform and Gaussian ones). It is shown that the electron beam structure can be longitudinally deflected by the geomagnetic field, and longitudinally elongated and transversely spread by the self-field effect. The deflection angle is mainly related to the strength of the magnetic field and the angle between the magnetic field and the beam longitudinal direction, while the elongation and the spread are mainly affected by the energy of the beam structure.