Single crystalline Ni gradient-diameter magnetic nanowire arrays (GDMNWs) with different D/d (the diameter of thick end (D) and thin end (d) of GDMNWs) were successfully prepared by constant potential electrodeposition into a tapered anodic aluminum oxide template. The TEM images of samples illustrated that the obvious gradient-diameter nanowires had been obtained. The HRTEM, SAED images and XRD pattern demonstrated that the nanowire arrays grew with Ni single crystal structures. The magnetic interaction of GDMNWs was investigated by first-order reversal curves (FORCs) and M(H) plots. The FORCs diagrams and M(H) plots of different D/d ratio were compared and indicated that the magnetic interaction of GDMNWs with a thin end was dominated by dipolar interaction, and the thick end was dominated by exchange interaction. There was a gradient overlap effect in dipolar interaction and exchange interaction between the thin end and thick end. The spatial distributions of such unique magnetic interaction of GDMNWs were likely to produce entirely new physical characteristics of memory effect and tunable ferromagnetic resonance.