The invention discloses a double-well construction method of a large gas storage in a high-impurity salt mine. The double-well construction method comprises the steps that a vertical well and a deviated well are excavated; the vertical well and the deviated well communicate; pipe cutting is conducted on the deviated well to form a salt cavern with the vertical well end being lower than the deviated well end; and gas is injected to the deviated well, so that bittern in the salt cavern is discharged out from the ground surface through the vertical well to complete construction of the gas storage. According to the double-well construction method, restriction of objective geological conditions is broken through, and the technical problem that in the prior art, a large salt cavern gas storage cannot be constructed in a high-impurity salt mine is solved.