The invention relates to a method for preparing Al-doped silicon carbide nanowires. The method is technically characterized by comprising the step of synthesizing a great quantity of Al-doped SiC nanowires on the surface of silicon-based ceramics by taking reaction-sintered silicon-based ceramics and graphite powder as precursors under the condition of no catalyst. With the method, a great quantity of high-purity Al-doped SiC nanowires is prepared at low cost and high efficiency. In addition, the shape and the dimension of the synthesized Al-doped SiC nanowires can be effectively controlled by regulating the preparation temperature. The synthesized nanowires mainly comprise a great quantity of diameter-variable 6H-SIC nanowires. The diameters of centerlines or center rods of the nanowiresare distributed within the range of 50-100 nm, the diameters of node structures on the centerlines or center rods are distributed within the range of 150-300 nm, and the nanowires are all constitutedby four elements including Si, C, Al and O. The lengths of the nanowires are controllable, and the longest nanowire can reach the magnitude order of millimeter.