In this study, the effect of different number densities of O-phase on the mechanical properties of the matrix B2 phase in Ti2AlNb alloy was investigated based on molecular dynamics. The results show that the yield strength and plasticity of the B2 phase are improved when the O phase is contained. This is because the precipitated phase hinders the start of the slip system in the matrix during the tensile deformation process, thereby improving the plastic deformation resistance of the B2 phase of the matrix. It is found that the improvement of material plasticity is mainly related to the release of internal stress, in which the release of internal stress by the B2 phase through martensitic phase transition is dominant, and the release of internal stress by dislocation is secondary. When the matrix B2 phase contains the O phase, the O relative dislocation hindrance will lead to stress concentration, thereby inducing martensitic phase transition of a large number of BCC structures, and the degree of stress concentration in this process decreases, delaying the growth of pore nuclei. On the other hand, since the O phase is a ductile phase, the growth of holes at the boundary between the O phase and the B2 phase is inhibited, so that the plasticity and toughness of Ti2AlNb alloy are greatly improved. And with the increase of the density of the number of precipitated phases, the yield strength and yield strain of the material decrease, but its strength and plasticity are still improved compared with those without the O phase. This is because, with the increase of O phase number density, the proportion of martensitic phase transition of the matrix atoms during the deformation process decreases, so the release degree of the stress concentration by the phase transition decreases, and the generation and expansion rate of the holes increases, so that the material is more prone to fracture failure.