A high-voltage automatic changeover switch, includes a support and a control circuit board mounted on the support. In one embodiment, the support includes an insulating frame, four high-voltage contacts mounted on each of two opposite plates of the insulating frame, four high-voltage contacts on the same plate being pair-to-pair arranged, the high-voltage contacts at the corresponding positions on the two plates being pair-to-pair arranged. A motor is provided on the support, and when switching the high voltages, the control circuit board controls the rotation of the motor to automatically switch the connection relation between the high-voltage contact pairs. Embodiments of the switch have a voltage-resistance of above 50 KV, allowing a pulse current of not less than 500 A to pass through, and good contact performance and a high stability. In one aspect, the high-voltage automatic changeover switch performs automatic switching of power source high voltages in an accelerator system, so that the accelerator obtains electron beams with different energies, thus allowing an expanded scope of application of the accelerator, including updating and upgrading of non-destructive testing systems, custom container inspection systems, and high-energy CT systems.