The wetting behavior of aluminum droplets (Al) on copper substrates (Cu) is studied numerically via the molecular dynamics (MD) approach, where an Al droplet spreads on a solid Cu surface, forming a liquid-solid interface. The key parameters are: 1. The size of the Al droplet; 2. The temperature of the Al/Cu systems; and 3. The crystal orientation of the Cu surface. The contact angles and equilibrium spreading radius of the Al droplet are measured. The results reveal that the temperature has a promoting effect on the wettability of the Al/Cu system, while the influence of the Al droplet size is negligible once it exceeds a critical value. The Al droplet demonstrates superior wettability on the Cu (111) surface due to its lowest energy barrier. The spreading of Al droplets on all Cu substrates primarily follows a two-stage process, with an initial fast regime driven by inertia and a subsequent slow regime governed by surface tension (on Cu (100) and Cu (110)) or diffusive force (on Cu (111)).