In recent years, the role of trace elements has attracted increasing attention, and the control of impurity elements has become stricter. Material research is developing towards high purity, high uniformity, and high precision. As is well known, inclusions have a significant impact on fatigue performance and stress corrosion resistance, especially in high-strength materials that are sensitive to notches. Therefore, foreign countries have increasingly strict requirements for the S, P content and inclusions of ultra-high strength steel. For example, the relevant technical standards in the United States stipulate that the S and P content of 300M steel must be less than 0 0.15%, and the sum of the two shall not exceed 0.025%. The control of S and P content in the factory is stricter, with a requirement of less than 0.006%, in order to ensure the superior performance of ultra-high strength steel and extend its service life.