Abstract: Co nanowires arrays were prepared by A.C electro-depositing Co²⁺ ion into the pore of a porous anodic aluminum oxide（AAO） template. A smooth surface(fluctuant degree was under ±10 nm/μm²) after the samples being mechanism polished and chemical polishing. The morphology properties of Co nanowire arrays were characterized by TEM, while the magnetic domain image was obtained by SPM. The each Co nanowire represented a single domain structure. The distribution of domain was corresponded to its morphology properties. The size of domain changed a little with the flying height of the magnetic tip. The observed domain structure would not change when the flying height of the magnetic tip was constricted to some range. All the domains reversed to one direction when the sample was magnetized under 2 T external field for ten minutes and the results were conformed to our micro-magnetization simulation results. The nearest domain had different magnetization direction, the same as the structure of quantized magnetic disk（QMD）. As the wire density was very high(10¹¹/cm²) in the as-prepared samples, the recording density was expected to be up to 100 Gbit/in² if each single domain can represent one bit of a binary data. It was very impressive to make such media into QMD as the preparing process was simple and low cost.