Abstract: Nuclear energy offers significant advantages, including cleanliness, high efficiency, stability, and large energy output, making it an indispensable energy source. As China advances its nuclear power capabilities, the demand for enhanced nuclear material performance grows. Traditional metallurgical processes, though effective, are complex and time-consuming. In contrast, additive manufacturing (AM) presents a promising alternative for producing nuclear materials due to its short production cycle, flexibility, and cost-efficiency. The microstructure of AM-produced metals differs significantly from those made through traditional metallurgy, exhibiting intrinsic features such as dislocation cells, sub-grain boundaries, and nano-oxides, which serve as radiation traps and improve resistance to radiation damage. However, AM-produced stainless steel also faces challenges, including coarse grains, anisotropy, and poor thermal stability. Adding small amounts of large atomic size elements like hafnium (Hf) to the alloy offers a potential solution to enhance radiation damage resistance and reduce microstructural defects. This study compared Hf-doped 316L stainless steel produced through AM and traditional recrystallization. Using various characterization techniques those include BSE, EBSD, EDS, and micro-Vickers hardness tests, the microstructure and mechanical properties of the two types of stainless steel were analyzed to understand the effects and mechanisms of Hf addition. Experimental results reveal that Hf addition significantly influences the material’s microstructure and mechanical properties, leading to grain refinement, an increased ratio of high-angle grain boundaries, more twin grain boundaries, reduced texture, and fewer second-phase particles as Hf content increases. Hf addition mitigates issues like coarse structure and anisotropy in AM materials while reducing grain boundary mobility and inhibiting the diffusion of Cr and Mo. This results in the disappearance of dislocation cell structures and element segregation at dislocation cell walls in AM 316L stainless steel. Moreover, increased Hf content enhances the hardness of both AM and recrystallized 316L stainless steel due to solution strengthening by Hf, Orowan strengthening from Hf-rich particles, and dislocation strengthening caused by geometrically necessary dislocations. After recrystallization, Hf-doped AM 316L stainless steel retains the excellent mechanical properties, improving the thermal stability of the printed samples. These microstructural and mechanical changes induced by Hf addition could enhance radiation damage resistance while maintaining mechanical performance, laying a solid foundation for future ion irradiation experiments.