Abstract: The corrosion behaviour and stress corrosion cracking of 2205 duplex stainless steel in H2S medium with and without CO2 were studied by u-shaped bending specimen soak, slow strain rate testing and electrochemical measurements. The fracture morphology after slow strain rate testing was observed by scanning electron microscopy. The results show that the existence of CO2 in the solution can reduce the pitting potential of the duplex stainless steel, increase the passive current density and corrosion current density. CO2 can promote the stress corrosion sensitivity of the duplex stainless steel, make the duplex stainless steel suffer brittle fracture clearly.