Abstract: Focusing on the challenge of cementing and sealing the cement sheath under layered gas injection conditions in Wenchang A Oilfield, this study delved into the corrosion of existing cement slurry systems in high CO₂ environments. From macro to micro levels, the mechanism of mechanical degradation of the cement sheath is revealed. The failure law of cementing and sealing under the joint influence of corrosion environment and wellbore load is explored. Based on the above achievements, an optimization idea for the cement slurry system is proposed, which features "high temperature resistance, pore filling, strength improvement, and elastic modulus control". The optimized cement slurry system meets the requirements of cement sheath sealing under layered gas injection conditions, and supports the smooth implementation of layered gas injection operations and safe and efficient development in Wenchang A Oilfield. It also provides reference for the development of oil and gas under similar complex geological conditions.