The utility model discloses a dissimilar metal submarine pipeline insulating device. The insulating device comprises a carbon steel lining corrosion-resistant alloy composite pipe used for being connected with a submarine pipeline needing corrosion-resistant treatment. The inner wall of the carbon steel lining corrosion-resistant alloy composite pipe is coated with an insulating coating. The thickness of a lining corrosion-resistant alloy layer, which is not coated with the insulating coating, of the carbon steel lining corrosion-resistant alloy composite pipe is equal to the sum of the thickness of a lining corrosion-resistant alloy layer, which is coated with the insulating coating, of the carbon steel lining corrosion-resistant alloy composite pipe and the thickness of the insulating coating. According to the insulating device, as the interior of the welded lining corrosion-resistant alloy composite pipe is coated with the insulating coating, galvanic corrosion of dissimilar metal is prevented; the device can be installed by adopting a conventional submarine pipeline laying method, and therefore the purpose of the device is achieved; as the inner diameter of the pipeline after being coated with the insulating coating keeps identical with the inner diameter of the composite pipe, the shearing impact on the insulating coating from conveyed material flow can be avoided, and the reliability of the insulating coating is ensured.