The invention discloses a carbon nano tube-doped ferric oxide three-dimensional nanometer material and a preparation method thereof, which relate to the technical field of the preparation of nanometer material. In the method, 1, 4 butylene glycol is used as a solvent, an acidified carbon nano tube is used as a doped phase, soluble trivalent ferric salt and ethylene diamine are used as raw materials, the materials are mixed at room temperature to form a uniform suspension, the uniform suspension is transferred into a mixed system to a stainless steel reaction liner, and stainless steel reaction liner is sealed for the uniform suspension to react in a baking oven at 150 to 200 degrees centigrade for 10 to 20 hours to obtain carbon nano tube-doped ferric oxide powder. The nano powder has a cuboid structure assembled by nano particles, and the cuboid has a length of between 0.1 and 0.5 mu m and a width of between 0.05 and 0.2 mu m. The method of the invention is simple. A solvent heating method is used for the first time to prepare a cuboid material assembled by doped ferric oxide nano particles of the three-dimensional carbon nano tube, thereby expanding the preparation field of the ferric oxide material.