A method for preparing a carbon/boron carbide composite material includes the following steps (A) providing a carbon compound, a carbon fiber, a boron compound and a binder to perform a pretreatment mixing procedure to form a precursor; (B) putting the precursor into a spray granulator for performing a granulation process and mixing the precursor to form an injection material with a uniform composition; (C) feeding the injection material into an injection molding machine for performing a compression molding process, thereby forming a carbon compound/boron compound green body; and (D) subjecting the carbon compound/boron compound green body to a two-stage heat treatment process to obtain the carbon/boron carbide composite material.