Abstract: By statistically analysing those accidents of gas trunk line at Sichuan OaS Field, the paper concludes that the internal corrosion is the main reason in pipeline accidents. In the article, such mechanisms and effects as even corrosion, pit corrosion, stress corrosion and erroded corrosion on the internal wall of pipeline have been explained and analysed, so that the corrosion controlling program for trunk line has been worked out. Thepractice shows that the internal corrosion of gas trunk line could be solved and that the pipeline life may be prolonged by adopting the protection of corrosive buffer.