Abstract: In an oil well, the 329th repair tubing fractured during throwing the string. By means of chemical compositions analysis, mechanical properties test, macro and micro fracture analysis, metallographic examination and force analysis, the fracture reason of the tubing was analyzed. The results show that the tubing was overload fracture. Because the tubing wall thickness was thinned seriously due to repair process and uniform corrosion, the bearing capacity of the tubing reduced greatly, which resulted in the tensile overload fracture of the tubing under the action of large load during throwing.