Abstract: The failure accident of tubing in a completion well tubing string for one HPHT natural gas well was investigated. the oil tubing corrosion and damage morphology can be obtained by appearance inspection and analysis of each oil tubing. The crack distribution rules on the outer wall of the oil tubing and the load born on the complement well tubing string were analyzed by PT and MT for oil tubing from different well depth. It was confirmed that oil tubing cracks were stress corrosion crack and corrosion fatigue crack by micro analysis on sampled crack of oil tubing. The causes of crack on oil tubing outer wall was analyzed and some suggestions for oil tubing to be prevented from failure were also proposed.