Abstract: There is a requirement in standard NB/T 20002.3, for class 1 components in Mn Mo Ni quenched and tempered steels, additional test specimens shall taken with a notch at 4mm from the fusion line. The paper analyzes it from three aspects of large impact test data, relevant standards and requirements, and organizations and performance characteristics in the HAZ. The results indicate that the optimization requirements of impact test in the welding procedure qualification for mechanical components of nuclear islands are reasonable.