The first-principles calculation method is used to study the alloy atom vacancy formation energies of O phase, B2 phase and α2 phase in TD3 alloy, and the energy stability and diffusion behavior of oxygen atoms in the three phases. The calculation results show that the vacancy formation energies of Al atoms in the three phases are all lower than those of Ti and Nb, which is beneficial to the formation of α-Al2O3 dominated oxide film on the surface of TD3 alloy. The interstitial energy of oxygen atoms in the octahedral interstitial positions of O phase, B2 phase and α2 phase is lower than that of tetrahedral interstitial positions, and the interstitial energy of titanium-rich octahedral interstitial positions is the lowest, the lowest oxygen atom interstitial energy is -5.0815eV respectively , -4.9425eV and -5.9315eV. The barriers to be crossed for oxygen atoms to diffuse along the best diffusion path in O phase, B2 phase and α2 phase are 0.812 eV, 1.913 eV and 1.164 eV, respectively.