The deformation mechanism and precipitation behavior of Al-5.8Cu-0.35 Mg-(0.3Sn) (wt.%) alloys were intensively investigated by microstructure characterizations and mechanical tests in this work. The experimental results showed that the added Sn elements can induce profound impacts on the alloys in three manners: (1) the formation of Mg₂Sn particles with excellent thermal stability can create particle-stimulated nucleation effect to facilitate dynamic recrystallization during hot deformation. Furthermore, the fine Mg₂Sn particles distributed at subgrain boundaries obviously inhibited the recrystallized grain growth during the solution treatment; (2) the suppression of natural aging was because there was insufficient releasing of vacancies from Sn-vacancy clusters at room temperature; (3) the accelerated artificial aging with lowered hardening effect was owing to both Sn-vacancy clusters inhibited the annihilation of quenching vacancies and reduced concentration of solute Mg consumed by the stable Mg₂Sn particles. Finally, the underlying mechanisms were elucidated in combination microstructure features with mechanical responses in the alloys.