With the expanding applications of NdFeB magnets, increasingly stringent requirements have been placed on their operational performance. Elemental doping is an effective approach to enhance these properties; however, the intrinsic microscopic mechanisms by which doping influences the magnetic moment and magnetocrystalline anisotropy remain unclear, limiting the development of high-performance, low-heavy-rare-earth NdFeB materials. In this work, first-principles calculations based on density functional theory (DFT) were systematically performed using the VASP software package. A Nd₈Fe₅₆B₄ supercell was adopted as the model system, and single-atom doping at the Nd sites (A sites, Nd₆M₂Fe₅₆B₄, M = Mg, Ni, Cu, Zn, Dy) as well as dual-atom co-doping systems (Nd₆MNFe₅₆B₄, M, N = Mg, Ni, Cu, Zn, Dy) were constructed. For all configurations, total magnetic moments, spin-projected density of states, magnetocrystalline anisotropy energies, and easy magnetization axes were quantitatively calculated and analyzed in depth. The results show that Ni single doping can reverse the magnetic moment of Nd at the 4g site, leading to a substantial increase in the total magnetic moment of Nd₆Ni₂Fe₅₆B₄ to 138.301 μB, whereas other single-element dopants have negligible impact on the total magnetic moment. The total magnetic moment is effectively enhanced in Nd₆CuMgFe₅₆B₄ and Nd₆CuNiFe₅₆B₄ due to the weakening of the Nd 4g magnetic moment and its coupling with Fe 3d orbitals induced by the dopants. Regarding magnetocrystalline anisotropy, Dy single doping reorients the easy axis from 111 to 100, while Cu-Ni co-doping induces a transition of the easy axis from 100 to 001 through synergistic elemental effects. Spin-projected density of states analyses confirm that the dopants modulate the hybridization between Fe 3d and Nd 4f orbitals, the local electronic states, and spin polarization near the Fermi level, thereby precisely controlling the evolution of magnetic moments and magnetocrystalline anisotropy. This study elucidates the intrinsic electronic mechanisms underlying doping-induced magnetic property modulation in NdFeB magnets, providing a reliable theoretical pathway and scientific guidance for the targeted design of high-performance NdFeB magnets with reduced reliance on heavy rare-earth elements..