Abstract: The gas pool of Member 2 of Xujiahe in West Sichuan was characterized by ultra-deep burial depth, high pressure and temperature, CO₂ bearing, and harsh operational environment has caused prominent wellbore failure. Statistics and analysis finds out that case wornout is the foremost element resulting in gas well wellbore failure in the Member 2 of Xujiahe in West Sichuan, followed by CO₂ corrosion, well head failure, galling and quality fault of case and so on. Based on the analytical result of the wellbore failure, combining corruption forecast to wellbore, calculation about residual intensity and analysis about string intensity, optimal design of well integrity has been proceeded from countercheck of case wornout, string corrosion control and well head device optimization. It has been applied preliminarily in Xinchang and Dayi gas field, and has acquired apparent application effect.