Abstract: Novel Al-Mg-Zn(-Cu) alloys exhibit broad application prospects to satisfy the urgent demand for lightweight and high-performance aluminum alloys in shipbuilding and rail transit fields. Nevertheless, a systematic understanding of the synergistic regulation mechanism of Cu content on strength and corrosion resistance is still lacking. In this work, Al-4.0Mg-3.0Zn-xCu alloys (x=0-1.5%, mass fraction) were taken as the research object. Hardness measurements, tensile tests, intergranular corrosion (IGC) tests and transmission electron microscopy (TEM) characterizations were conducted to systematically reveal the coupled effect of Cu content on age precipitation behavior, mechanical properties and intergranular corrosion resistance. The results show that increasing Cu content remarkably accelerates the age-hardening response, and the peak-aged hardness rises from 99.0HV to 159.8HV. When the Cu mass fraction reaches 1.5%, the alloy obtains a yield strength of 386 MPa while maintaining an elongation of 20.6%, realizing the synergistic optimization of high strength and high ductility. Its comprehensive mechanical properties outperform existing commercial aluminum alloys for ship and rail transit service. In terms of corrosion resistance, raising Cu mass fraction to 1.5% changes grain boundary precipitates into discontinuous distribution and narrows the width of precipitate-free zone (PFZ), which significantly improves the resistance to intergranular corrosion. The underlying reason is that high Cu addition reduces the formation energy and critical nucleation radius of precipitates. It facilitates the nucleation and precipitation of T″ phase and effectively inhibits the segregation of solute atoms at grain boundaries. These results provide a theoretical basis for composition design and microstructure control of high-performance Al-Mg-Zn(-Cu) alloys applied in ships and rail transit.