Abstract: The fractured high temperature bolt used for high-pressure outside cylinder in some power plant was investigated by means of macro-morphology inspection, chemical composition analysis, microstructure analysis, mechanic performance testing, fracture morphology analysis and energy-dispersive X-ray analysis. The investigation showed that due to improper manufacturing process, the grain was coarse in local region of the bolt and its impact ductility was insufficient, thus under act of impact load the bolt occurred brittle fracture in region of stress concentration. Put forward the preventive suggestions as strengthening the technical supervision and regulating strictly, to prevent the similar fracture.