Abstract: To understand the propagation law of relativistic electron beam in vacuum, the propagation process of relativistic electron beam based on the Lorentz transform in special relativity were simulated in this paper. The spatial electromagnetic field distributions during long-range propagation of relativistic electron beam were analyzed. And the variation law of electron beam radius with propagation distance was explored by phase space theory . The results show that the electric field generated by charges moving at relativistic velocity is no longer spherically symmetric, but tends to be concentrated in the vertical direction of charge motion. The radius of the relativistic electron beam increases exponentially at the beginning of the propagation process, and then become linearly growth after a certain distance of propagation. Compared with conventional methods, the Lorentz transform has efficiency advantage in processing high-energy electron beams, which helps to solve the issue of longer computational hours due to the large spatial size of the relativistic electron beam long-range propagation model.