The structure and magnetic properties of fcc-Fe/Cu (100) superlattices have been investigated by the first-principles total energy calculation based on density functional theory (DFT). Through the optimization of the structure of Fe/Cu superlattices, it has been found that the interlayer spacing of Cu layers is contracted while the interlayer spacing of Fe layers is expanded. There are no obviously changes of Fe/Cu interfaces for Fe3Cu3 and Fe3Cu5 models. The layer spacing for Fe3Cu5 changes larger than that of Fe3Cu3 model, which results to a slightly larger magnetic moment of FeCu5 than that of Fe3Cu3 model. We also analyze the density of state near the Fermi surface and calculate spin asymmetry factor of each layer in Fe/Cu systems. Based on the two-current model, we evaluate the magnetoresistance ratio 21.8% for Fe3Cu3 and 22.8 % for Fe3Cu5 system.