Wet gas and solution environments containing H2S/CO2 were simulated in a high temperature and high pressure autoclave. Corrosion behaviors of API-X60 pipeline steel were investigated with Scanning Electron Microscopy (SEM) and X-ray Diffraction methodology (XRD). Effects of high H2S partial pressure on corrosion rate and scale were discussed. The results show that corrosion rate increased with H2S partial pressure in wet gas but raised up first and then dropped down in the solution immersion environment. Pitting corrosion was observed at the situations with H2S partial pressure 2.0MPa. The corrosion process was controlled by H2S and mackinawite (Fe1＋XS) was the dominant composition in the corrosion products free of FeCO3. Pitting was occurred in the scale’s defect which was acidified by the HS- and Cl- ions migrating, and the development of the pitting was affected by the electrochemical property of the sulfur-rich phase and FeCl2 admixture. The crystal morphology and structure were more complicated in the scales formed in immersion environment, which were less integrated and bonded than that formed in wet gas. However, hydrogen blistering and hydrogen-induced cracking were more easily occurred for X60 in wet gas than that in immersion environment.