Abstract: Due to the high CO₂ content in high-pressure sections of some wells in Yingqiong Basin, the strength degradation of cement sheath and the mechanism of strength reduction of cement caused by CO₂ corrosion are not clear under the condition of high temperature and high CO₂ content, the effects of corrosion time, temperature, pressure and CO₂ partial pressure on the corrosion of cement were analyzed by experimental method, and the corrosion mechanism was analyzed. The results show that with the increase of corrosion time, temperature, CO₂ partial pressure and formation pressure, the corrosion depth of cement increases, while the compressive strength decreases. The main reason for this phenomenon is that CO₂ dissolved in water corrodes tobermorite and xonorite in cement, generating calcium bicarbonate which is easily soluble in moist CO₂ environment, so that the porosity and permeability of cement increase and the strength decrease. This study provides a basis for the selection and improvement of cement slurry system for subsequent high temperature and high pressure wells.