Abstract: The Z40CSD10 steel exhaust valve of a certain marine engine broke after approximately 18 000 hours of service. The reasons for the fracture of the exhaust valve were analyzed using macroscopic observation, chemical composition analysis, scanning electron microscopy and energy spectrum analysis, mechanical property testing, metallographic examination. The results show that the fracture property of the exhaust valve was fatigue fracture, which originated from the corrosion pit of the exhaust valve disc. The fractured exhaust valve experienced high-temperature oxidation corrosion on its surface due to prolonged exposure to high-temperature flue gas, and the flue gas contained a high content of corrosive media S and Cl elements, which accelerated the formation of corrosion pits and ultimately led to fatigue fracture of the exhaust valve.