In the paper, the process of TC4 aging phase transition and diffusion bonding was studied by molecular dynamics method. the radial distribution function of TC4 ternary alloy and the relative content of different crystal structures were analyzed. At the same time, the atomic concentration distribution, diffusion connection width and diffusion coefficient of diffusion bonding process under different thermal insulation temperature are studied. The results show that the structural changes of TC4 in the aging phase transition are mainly manifested in the new a phase of metastable b phase, and the b phase content reaches 23% after the state stabilizes, which is in good agreement with the experimental results. In the process of TC4 diffusion, the titanium atoms near the interface are mainly diffused, and vanadium atomic diffusion is secondary, while aluminum atom is relatively few. Under the same conditions, the diffusion connection width and thermal insulation temperature are in a good linear relationship. The diffusion coefficient of titanium is exponentially related with the temperature of heat preservation, and the results are in accordance with the experiment.