Abstract: As the thread in the primary manway of the steam generator of Qinshan phase II nuclear power plant was damaged, the reason was analyzed in terms of material, stretching and equipment maintenance. Mechanical properties of the wire thread insert were studied and the thread is repaired by the thread wire technology. The test result shows that the stretching of the bolt installed with wire thread insert meets the requirement, and the engineering application of the thread wire technique on the steam generator can provide a reference for solving the similar problems in other nuclear power plants.