The present invention relates to the field of the oil field gathering and transportation dehydration technology, especially to a high-impedance alternating current and direct current superposition high-voltage power supply device for crude oil electric dehydration. The device comprises two high-voltage generation loops; a direct current high-voltage generation loop is formed by an alternating current voltage regulation module, a current limitation reactor, a boosting transformer and a high-voltage rectification unit, and outputs high-voltage direct current between an output end HVout1 and an output end HVout 2; an alternating current high-voltage generation loop is formed by an alternating current voltage regulation module, a current limitation reactor and a boosting transformer, and outputs the alternating current high voltage between the output end HVout 2 and a GND; and the two high-voltage generation loops output high-voltage waveform of direct current superposition alternating current between the HVout 1 and the GND through a series superposition mode. The formation of stable conductive water ripple in a high water content crude oil emulsion may be effectively eliminated so as to ensure the stability of a dehydration electric field, improve the dehydration efficiency of the crude oil and reduce the water content of the dehydrated crude oil.