The invention relates to a switch, in particular to a high voltage automatic change-over switch comprising a bracket and a control circuit board. Four high voltage contacts are respectively installed on two opposite faceplates on a U-shape insulation support of the bracket; a motor is positioned on the bracket; the output axle of the motor extends inside the U-shape insulation support; two rotors coordinates with the high voltage contacts are respectively at the end section of the motor; a position contact block is positioned on the output axle of the motor; two position limiting switches that coordinate with the position contact block are positioned on the bracket. The beneficial effects of the invention are: capable of resisting the voltage of more than 50KV, allow the passing of pulse current of no less than 500A, excellent contact performance, high stability and capable of automatic change-over. Therefore, the invention, which is able to realize the automatic change-over of power source high voltage in an accelerator system, ensures accelerator to acquire electron flow with different energies, enlarges the application scope of accelerator, thus bringing important significance to the upgrade of industrial non-destructive inspection, customs container detection system and high energy CT system.