Abstract: Nickel-based superalloys exhibit excellent load-bearing and high-temperature resistance and are widely used as key materials for hot-section components in aerospace equipment. However, traditional high-strength nickel-based superalloys are prone to crack defects during additive manufacturing due to strong constraints and rapid non-equilibrium solidification processes, severely limiting their applications. Segregation of key alloying elements during the final stages of solidification is the primary factor influencing crack formation. This review focuses on the Hafnium element (Hf) in typical difficult-to-print γ′-strengthened nickel-based superalloys (i.e., CM247LC), emphasizing its significant impact on the solidification temperature gradient and its effect on crack sensitivity in additive manufacturing of high-temperature alloys. Further discussion is provided on the influence of Hf on the heat treatment microstructure evolution and high-temperature mechanical properties of various nickel-based high-temperature alloys manufactured through additive processes. This review highlights the importance of appropriately adjusting the content of key elements and establishing nickel-based superalloy composition design guidelines suitable for laser additive manufacturing technology, to support the development and application of high-performance nickel-based high-temperature alloys through additive manufacturing.