By screening of the inhibitor, the initiator and the modifier of the channeling sealing agent, a CO₂ gas flooding channeling sealing agent which had excellent properties and was suitable for high temperature and low permeability oil reservoirs was developed. The composition of the channeling sealing agent is as followed: the dosage of AM was 4.5 % (mass fraction), of initiator was 0.25%, of modifier was 0.3% and of inhibitor was 0.5%. At room temperature, the viscosity of the channeling sealing agent solution is 1.1 mPa·s, hence, it was easy to be pumped and injected. At 100℃, the gelling time was controlled within 2.5-12 hours through changing the dosage of inhibitor, and the viscosity was above 120×10⁴ mPa·s accordingly. For the channeling sealing agent in salinity of 57728.92 mg/L, its viscosity was more than 170×10⁴ mPa·s when the pressure of CO₂ reached 8.0 MPa at 126℃. In a sand pack with a length of 120 cm, a diameter of 25cm and the permeability of 1.631 μm², the pressure of injection water is about 0.08 MPa, and the pressure of CO₂ flooding was around 2.2 MPa after gelation. In a word, the system was easy for injection, and had a strong plugging ability for CO₂ gas flooding. The parallel core experiment showed that the system had good performance of sealing channeling for CO₂ and the EOR could be further improved by 5.1%.