Nearly monodispersive nickel 3D nanostructures were synthesized using a improved hydrothermal route with poly-(N-vinyl-pyrrolidone) as capping reagent. The obtained products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and field-emission scanning electron microscopy (FE-SEM). Results reveal that cubic nickel crystals possess flower-like 3D nanostructures with nanospearheads growing radially from the core and a uniform diameter of about 1.5 μm. These nanospearheads have almost uniform shapes: the root in (120±20) nm, the tip in (15±5) nm, the length in (400±50) nm, and the thickness in (10±2) nm. Contrast experiments demonstrate that flower-like shape of nickel 3D nanocrystals is controlled by the cooperative effects of time, temperature and surfactant. The good catalytic effects indicate these flower-like nickel 3D nanocrystals are likely to be applied as a better catalyst in the future.