In this work, surface enhanced Raman spectroscopy (SERS) substrates with Ag nanoparticles (NPs) decorated Co₃O₄nanowires (NWs) grafted on the three-dimensional (3D) network architecture of Ni foam (denoted as Ag-NP@Co₃O₄- NW/Ni-foam) arrays are manufactured. In the experiment, the hierarchical Ag-NP@Co₃O₄-NW/Ni-foam arrays exhibit strong SERS activity due to the higher density of the “hot spots” created from the large quantities of neighboring Ag NPs. Using this hierarchical 3D SERS substrates, the crystal violet (a banned drug of aquaculture) with concentration down to 10^-14mol/L can be detected, which shows potential application in SERS-based rapid trace-level detection of harmful food additives.