Abstract: The cracking reason of the exhaust valve turbulent hood at turbine side of a nuclear power plant was analyzed by fracture morphology observation, chemical composition test, microstructure analysis and mechanical performance test. The results show that the cracking mode of the turbulent hood was fatigue brittle cracking. The chemical composition of material did not meet the standard, which reduced its strength. The positioning holes on the upper end of the turbulence hood were not centered during installation. The wear and vibration produced by the airflow during working process made a relatively large stress concentration in this location, leading to crack initiation in outer flange surface of the turbulence hood. Under long-term cyclic thermal stresses, the cracks propagated along the section with the smallest bearing capacity, leading to cracking of the turbulent hood. It was suggested to take material re-inspection measures , thereby reducing the inflow of unqualified materials and to take strict requirements for installation process to avoid misalignment, thereby reducing stress concentation caused by wear and vibration.