Abstract: The P110 tubing as used in a certain CO₂ test injection well broke and failed during the operation. The failure causes for the pipe body are analyzed by means of testing of the chemical composition and the mechanical properties，the metallographic examination，microscopic morphology of the fracture surface，corrosion product（EDS）analysis and macroscopic morphology observation. The results show that in the annular space containing corrosive medium such as sulfide and chloride，under the action of the local stress，stress corrosion cracking（SCC）occurs in the tubing，and continuously expands which inevitably leads to the fracture failure of the pipe.