The aerospace vehicles will encounter the radiation of space electrons when they are operating in extraterrestrial space. Establishing an electronic source on the ground to simulate the electronic environment, which is encountered by the aerospace vehicle in space, and to study the damage caused by related effects and the effectiveness of protective measures is an important method to ensure the safe and stable operation of aerospace vehicles. The ground simulation facility of the space electronic environment directly provides electrons in the energy range of 1.5 MeV by an electron linac, followed by a transport system to expand the electron beam size. The large energy range demands higher requirements for the design and operation of the accelerator. This paper mainly investigated the design and implementation process of the accelerator. The energy switching technology was adopted and the beam loading effects were considered. The energy switch accelerating tube consists one bunching cavity and five light speed cavities. When the energy switch is turned on, there are acceleration fields in all six cavities. When the energy switch is turned off, there are acceleration fields in the first three cavities. The beam dynamics calculation was carried out using PARMELA. The dynamic shows the electron beam can be effectively accelerated in two states, with high energy of 5.05 MeV and low energy of 0.98 MeV. The emission angle at output is less than 140 mrad, which meets the subsequent transmission requirements. Coupling characteristics under different conditions were studied. Based on the analysis and calculation of beam loading effect, input power and coupling coefficient, the coupling coefficient is determined to be 3 at the low energy level, and corresponding pulse beam current is 300 mA. The coupling coefficient of high energy level is 1.5, and corresponding beam load is 300 mA. Meantime, the magnetron-based power source output parameters were analyzed and the corresponding experimental research was carried out. The output pulse power of magnetron is adjusted from 0.7 MW to 1.8 MW, and the stability and energy spectrum of high power output can meet the demand. After the installation and commissioning of the accelerator, the energy was measured by the polyethylene dose depth distribution method. The results show that the test energy reaches 5 MeV when the pulse current is 94 mA, and the energy is 0.9 MeV when the pulse current is 334 mA. The experimental test results of the accelerator show that the electron beam meets the requirements and provides an effective and reliable electron source for the simulation device.