Abstract: An on-the-site investigation is made into the failures of the thread galling and jump-out of the Φ73.02 mm×5.51 mm N80-Q externally-upset tubings as used in a certain oil well,while visual analysis of the samples taken from the faulty pipes is also conducted. An all-round inspection is made to the processing quality of the thread connections of the said tubings,and relevant physical-chemical tests of the tubings' material are performed,too. Moreover,systematic tests are carried out to the make & break performance and the tensile property of the tubings. Base on the results of the above mentioned analysis and tests,it is identified that the galling fault is caused by maloperation,and the jump-out fault is resulted in by reduction of the connection strength as following the galling,which has nothing to do with the thread processing quality and material of the tubings that are in compliance with applicable standard requirements.