The invention discloses a carbon dioxide corrosion inhibitor used for oil and gas wells, and a preparation method and applications thereof, and belongs to the field of oil and gas well corrosion prevention. The carbon dioxide corrosion inhibitor used for oil and gas wells comprises, by weight, 30 to 60 parts of thioureido amide, 20 to 40 parts of isopropanol, 5 to 25 parts of a surfactant, and 10to 30 parts of water. The chemical structure of thioureido amide is disclosed in the invention, wherein n=2, 3, or 4, R1 is used for representing C11-C17 alkyl. The carbon dioxide corrosion inhibitoris simple in composition, and low in cost, is capable of reducing corrosion rate of CO2 on oil and gas wells, is suitable to be used at 20 to 120 DEG C, and is high in stability.