With H2C2O4?2H2O as precipitant and NiSO4?6H2O as Ni source, NiCO4 precursor was prepared through coprecipitation method in the first step. Afterwards, highly regular sub-micron spherical Ni powders were calcined and reduced under H2 atmosphere at middle temperature in the second step. Scanning electronic microscopy, X-ray diffraction and laser particle size analyzer were used to characterize the morphology and microstructure of Ni powder. The results show that the purity of Ni powder is very well. The secondary particle of Ni powder is about 40μm agglomerated with a lot of 0.5μm dispersed and uniform primary particles, which guarantees the excellent forming property and sintering activity. The crystallinity of Ni powder increases with the sintering temperature. The optimal preparing parameters are 0.7mol.L-1 Ni2+ concentration, 40℃ reactive temperature and 500℃ sintering temparature. Grain growth activation energy of Ni powder can be calculated as 26.9 kJ?mol-1 according to the relationship between grain size and sintering temperature and Ni powder’s growing mechanism is interfacial diffusion controlling mechanism.