The work aims to study the microstructure evolution of Ni-Al diffusion couple in the thermal diffusion process so as to put forward a formation model of Ni3Al alloy honeycomb. Ni was electroplated on the surface of easily processed Al honeycomb so as to study the influence of thermal diffusion temperature and time on the Ni-Al honeycomb microstructure. The phase composition of Ni-Al diffusion couple was analyzed by X-ray diffractometer. The section of Ni-Al diffusion couple was analyzed by scanning electron microscope and energy dispersive spectroscopy technique, and the microstructure evolution of Ni-Al diffusion couple was speculated. Through the analysis of the microscopic morphology, energy dispersive spectrum elements and X-ray diffraction of Ni-Al diffusion couple after thermal diffusion, it was found that NiAl3 appeared in the Ni-Al interface, and then disappeared, therefore a multilayer solid structure with Ni2Al3 as the main diffusion layer and NiAl and Ni3Al as the transition layer formed, with the extension of thermal diffusion time, at a thermal diffusion temperature of 500 ℃. At a thermal diffusion temperature of 700 ℃ and 1100 ℃, Ni-Al diffusion couples formed a multilayer hollow structure with Ni2Al3 and NiAl as the main diffusion layer, thin NiAl and Ni3Al as the transition layer and pure Ni as the shell. At a thermal diffusion temperature of 1300 ℃, with the extension of diffusion time, the Al-phase intermediate layer transformed a three-phase mixed structure of Al, NiAl3 and Ni2Al3 into single-phase Ni2Al3 and NiAl structure with uniform composition in turn. With the diffusion time continuing prolonging, the Ni layer was exhausted. Finally, The Ni-Al diffusion couple formed a Ni-Al alloy with γ′-Ni3Al as the strengthening phase. In conclusion, Al atoms significantly diffuse outward in the Ni-Al solid phase diffusion process with the temperature increasing. Ni atoms significantly diffused inward in the Ni-Al solid-liquid diffusion process with the thermal diffusion time extension. After annealing at 1300 ℃ for 1h, the Ni3Al-based alloy honeycomb is successfully prepared.