This research explores a novel staggered serrated slat-cusp design concept for slat noise reduction across 3∘~9.5∘ angles of attack (AoAs). High-order wall-resolved large-eddy simulations (WRLES) are executed for serrations with 60∘ and 80∘ stagger angles on the 30P30N high-lift airfoil under Re=1.71×106. Far-field acoustic signals are predicted through the Ffowcs Williams-Hawkings (FW-H) acoustic analogy method. The computational method is validated through good agreement with multiple experimental datasets on pressure coefficient ( Cp ) distributions, wall pressure spectra, and far-field noise spectra across 3∘, 5.5∘, and 9.5∘ AoAs. The acoustic results establish that staggered serrated slat-cusp effectively attenuates slat tonal noise via simultaneous suppression of tonal noise sources intensity (exceeding 4.4 dB reduction for the 80∘ staggered angle configuration) and their spanwise constructive interference, yielding overall noise reductions of around 1.7 dB and 1.8~2.3 dB for 3∘ and 5.5∘ AoAs, respectively. However, under high-incidence condition, while tonal noise attenuation continues, the concomitant increment of mid-low frequency broadband noise and its associated spanwise constructive interference enhancement partially offset these benefits, resulting in 0.6~0.7 dB overall noise elevation versus the baseline. Nevertheless, superior aeroacoustic performance is consistently demonstrated for the larger stagger angle configuration. Furthermore, aerodynamic penalties remain negligible with lift degradation below 0.56% across all tested conditions, validating the implementation feasibility of this passive noise reduction technology for high-lift systems.