The invention belongs to the technical field of metallic oxide nanometer materials, and particularly discloses a ferroferric oxide nanometer material and a preparation method thereof. The preparation method disclosed by the invention comprises the following steps: preparing an amorphous ferric oxide precursor by adopting an anodic oxidation method; carrying out a catalytic reaction between the precursor and a mixed solution of hydrazine hydrate and purified water at a low temperature, enabling the amorphous ferric oxide to convert into ferroferric oxide, thereby obtaining the sheet hexagonal ferroferric oxide nanometer material with surface gaps. The ferroferric oxide nanometer material prepared according to the invention has the surface gapped sheet hexagonal shape and has good crystallography characteristics and rough surface shape. The ferroferric oxide nanometer material is enabled to have wide application prospects in the fields of photocatalysis, solar photovoltaic devices and the like. The nanometer material disclosed by the invention is soaked by the purified water at the low temperature and has the advantages of high production efficiency, low synthetic cost, simple process requirements and the like.