1. A method of generating a three-dimensional (3D) model file, the method comprising: generating a region field defining information associated with a printing material of a 3D model; and generating a material field defining the printing material, wherein the region field comprises the material field, a color texture coordinate index field defining coordinate indexes of color texture, and a material texture coordinate index field defining coordinate indexes of material texture, and wherein when the material texture coordinate index field is null, the color texture coordinate index field is used as the material texture coordinate index field.