The utility model relates to the field of tertiary oil recovery in oil fields, belongs to an injection non-return device for a CO2 injection well, and provides a device for preventing high pressure CO2 gas form flowing backwards in the well when the injection of a wellhead of the CO2 injection well is stopped. The device mainly comprises flange valves 1, flanges 2, an upper joint 3, an upper jacket 4, a bull plug 5, a regulating ring 6, a spacing ring 7, a fixing pin 8, a retaining ring 9, a spring 10, a centering sleeve 11, a valve 12, a connecting sleeve 13, a valve seat 14, an L-shaped packing 15, a protective wire 16, a lower jacket 17 and a lower joint 18, wherein the upper joint 3 is connected with the upper jacket 4; and the connecting sleeve 13 is in threaded connection with the lower jacket 17. The device has the advantages of simple structure, CO2 corrosion resistance, small throttling, reliable gas sealing performance under high temperature, and high pressure and the like.