Abstract: Abnormal tension occurs on the main pump snubber tie rod of a nuclear station  when it is loaded by bolt stretcher. In order to solve this problem, this paper uses the methods of cause elimination and analytical calculation to diagnoze the fault. It is identified that the main reason for abnormal tension is the short thread length. In view of this problem, the scheme of adjusting the screw thread length is proposed and verified by the finite element method, and the stress analysis of the anchor rod thread also meets the requirements of the code. The handling of this event can guarantee the construction progress on site and avoid great economic loss.