<p>The efficiency and safety of nuclear power plants heavily depend on the cooling water circulation system and its critical components, especially the valve rod in seawater gate valves. Repeated failures and frequent downtime maintenance of the valve rod significantly impact the efficiency and safety of the drainage process in nuclear power plants. A comprehensive failure analysis was conducted on the abnormal fracture of the seawater gate valve rod in a nuclear power plant. Commissioned by the plant, material inspections, microstructural analyses, and a comprehensive evaluation were performed. Although the valve rod material meets standard specifications, material defects such as inclusions were found to be the primary factors leading to fatigue crack initiation within the matrix. When these material defects reach a critical size, fatigue cracks initiate and propagate from these defects, which is identified as the root cause of valve rod failure. Based on this finding, improvements in design, manufacturing, and installation processes are proposed. The research provides crucial insights for ensuring the safe and stable operation of seawater gate valves in nuclear power plants.</p>