The invention discloses an iron oxide-carbon nanotube ternary composite material and a preparation method thereof. According to the method, Fe3O4 and Fe2O3 particles with controllable shapes and components are evenly distributed in a three-dimensional network of a carbon nanotube. The method comprises the following steps: firstly, evenly dispersing the functionalized carbon nanotubes and iron salt in deionized water; then adding an alkaline solution into the deionized water and regulating the pH (Potential Of Hydrogen) of the mixed solution; performing hydrothermal reaction on the mixed solution in a reaction kettle; cleaning and drying an obtained precursor; and finally, calcining an obtained product so as to obtain a Fe3O4-Fe2O3-carbon nanotube ternary composite material in a shape of black powder. The method has the advantages of simplicity, safety, environmental protection and no pollution in preparation process. The prepared Fe3O4-Fe2O3-carbon nanotube ternary composite material is good in structure stability and monodispersity. When the Fe3O4-Fe2O3-carbon nanotube ternary composite material is taken as a negative electrode material of a lithium ion battery, the discharge capacity of the composite material exceeds 1000mAh/g; the composite material is long in cycle life and good in rate performance.