Abstract: Aiming at the fracture problem of the threaded rod of the inlet header of the high temperature reheater of an ultra supercritical 1000 MW unit, macroscopic analysis, composition inspection, hardness inspection, room temperature tensile property test, metallographic structure analysis and fracture morphology analysis were carried out on the threaded rod. The test results show that there is an obvious necking phenomenon near the cross section of the threaded rod, there are creep cavities on the whole fracture surface, the creep cavities grow up, aggregate and form creep cracks. After the installation of temperature measuring points, the measured temperature in the roof enclosure exceeded the original design value by a large margin, and the calculated value of the axial stress of the threaded rod exceeded the standard at the measured temperature, under the action of high temperature and high stress, creep fracture of the threaded rod occurs at the root of the tooth where the stress is concentrated。