5d transition metal Hf, Ta, W, Re and Ir is widely used in Ni-based single-crystal (SC) superalloys of the fourth and fifth generation, but for the mechanism, there is no theoretical and comprehensive research. Equilibrium lattice constant, formation enthalpy, cohesive energy, density of states, electron density difference and electronic populations of the pure and the 5d transition metals Hf, Ta, W, Re and Ir doped Ni3Al were studied by the plane-wave ultrasoft pseudopotential method based on the density functional theory. The calculations show that the occupational site of 5d transition metals Hf, Ta, W, R and Ir are of the Al site after doping; strongly orbital hybridization between the orbital electron of Ni 3d and Al 3p occur after Hf, Ta, W, Re, Ir doping, which lead to the bound electrons, smaller delocalization and narrower peak; Ni atoms and the first nearest neighbor Al atoms are covalent bonds in pure Ni3Al; however, Ni atoms and the first nearest neighbor X(Hf, Ta, W, Re, Ir) atoms are covalent bonds, which are gradually increased with the enlargement of atomic number of 5d transition metals.