Abstract: The microstructure transition process of Ni-5%Cu alloy is researched in therange of 2.6-130K/S cooling rate with zone melting unidirectional solidification technique. It is indicated that the solidified morphology transits from dendrite to superfine cell within the limitids of the crystal growth velocity 500~700μm/s. The temperature gradient has a great effect on the microstructure in hyporapid solidification. The crystal growth orientation is an important factor to the selection on the solidified microstructure.