The invention discloses an exploitation method of a horizontal SAGD well pair and a SAGD oil well system. The exploitation method includes following steps: injecting gas into a gas injection well of the horizontal SAGD well pair; when a steam cavity ascends to the top of an oil layer and enters a transverse expansion stage, connecting high-voltage high-frequency alternating current to a conductive cable arranged in a U-shaped horizontal well to heat the oil layer, wherein a horizontal section of the U-shaped horizontal well is arranged between two adjacent horizontal SAGD well pairs or arranged in one horizontal SAGD well pair; according to transverse expansion parameters of the SAGD steam cavity, adjusting the alternating current, and continuing heating the oil layer; when the SAGD steam cavity descends to a preset height, disconnecting the conductive cable in the U-shaped horizontal well so as to stop heating the oil layer. The exploitation method further increase recovery ratio and has economic benefit obviously better than common steam injection SAGD.