Abstract: To address the CO₂/H₂S corrosion of low-carbon micro-alloy steel which is used in expandable tubular，based on electrochemical experiment，weight loss method and SEM，the authors of this paper research the corrosion performance and the law of the low-carbon micro-alloy steel under the conditions of H2S only(pH=2.9)，CO₂/H₂S ( 1∶1，pH=2.9) and CO₂/H₂S (1∶1，pH=5.3).The experimental result indicates that the corrosion rate of low-carbon micro alloy steel will increase at the condition of H₂S only，as the sulfide of iron is yielding.The corrosion rate reduces when CO₂ existence，because CO₂ is adsorbed in the steel surface and the compact protective film is formed.As
the uneven organization and the Segregation of MnS，sample surface is roughness，corrosion product films exist microcracks，pH value lowers，the rougher specimen surface is after corrosion，the more serious corrosion is.

Key words: CO₂/H₂S corrosion, low-carbon micro-alloy steel, corrosion mechanism, weight loss method, electrochemical method, SEM