<p>Based on molecular dynamics simulation, the tensile mechanical properties and plastic deformation mechanisms of nanomaterials with twin boundaries located at different positions are studied in this work. The tensile simulation results show that twin boundaries located several layers of atoms underneath the surface are beneficial to the improvement of the material’s yield strength. This phenomenon is manifested in various metallic materials with different stacking fault energies and under various loading conditions. Further calculation of the reaction path of dislocation nucleation shows that twin boundaries beneath the free surface can inhibit the deformation mechanism of surface dislocation nucleation, and the initial plastic deformation occurs in the form of internal dislocation loop nucleation. The calculation results also indicate that the nucleation of dislocation loop inside the material requires higher activation energy and activation volume, which suppresses the initial plastic deformation in the material and thus improves the material’s yield strength. These findings will shed light on the understanding of mechanisms of twin boundaries induced the surface strengthening.</p>