<p>In this study, molecular dynamics (MD) simulations were employed to investigate the tensile behavior of polycrystalline Ti alloys. Particular attention was paid to the effects of nanopores on strength, ductility, and elastic modulus, focusing on microstructural evolution and stress distribution at the atomic scale during stretching. In addition, the coupling effect of grain size and pore size was analyzed. The findings indicate that the influence of nanopores on the mechanical response of polycrystalline Ti alloys is governed by a critical pore size. When nanopores are smaller than this threshold, the material exhibits high strength and ductility, whereas nanopores exceeding the critical size lead to a pronounced decline in both strength and ultimate strain. Different macroscopic mechanical properties correspond to distinct micro-evolutionary mechanisms, with stress concentration arising from nanopores playing a key role. Moreover, an energy-based perspective was used to explain why the critical pore size varies with grain size. The results suggest that grain boundaries can mitigate internal defects to some extent, thereby enhancing material strength and offering new insights into fine-grain strengthening.</p>