Abstract: Fracture occurred at 8 m below the coupling of P110S steel grade tubing in an oil well. The causes of tubing fracture were analyzed by macroscopic observation, chemical composition analysis, metallographic examination, scanning electron microscopy and energy spectrum analysis, X－ray diffraction analysis and other methods. The results show that the mechanical properties of the tubing were unstable, and the corrosion products on the fracture of the tubing were mainly FeS. The high strength, low service temperature and large mass of the tubing led to the formation of sulfide stress corrosion cracking inside the tubing.