The invention belongs to the technical field of oil field oil recovery techniques and particularly relates to a CO2 corrosion preventing method and device of a CO2 flooding oil injection well shaft. The CO2 corrosion preventing device comprises a detecting unit installed in an oil jacket annulus and used for detecting CO2 amount and further comprises a computer, a CO2 discharging unit and a corrosion inhibitor adding unit, wherein the CO2 discharging unit and the corrosion inhibitor adding unit are respectively communicated with the oil jacket annulus, and the detecting unit, the CO2 discharging unit and the corrosion inhibitor adding unit are electrically connected with the computer. The CO2 corrosion preventing device of the CO2 flooding oil injection well shaft performs corrosion prevention from two aspects of degassing and corrosion inhibitor adding, achieves the functions of field automatic exhausting, chemical adding and the like, is convenient to operate, practical, quick and convenient, can retard the corrosion to an injection well casting and an injection pipe column and meets the requirement of a CO2 flooding test field.