Abstract: The fracture cause for stent of valve in power station was analyzed by macroscopic examination, chemical composition analysis, tensile test, impact test, metallographic analysis, fracture analysis and comprehensive analysis. The results show that the fracture cause was brittle fracture caused by material strength is not enough to work under normal and operating load, because there are serious casting defects, such as inclusions, shrinkage cavity, casting cracks. Finally, the preventive measures are put forward for fracture cause.