The invention provides a method for preparing a titanium-diboride-based ceramic composite material in order to solve problems existing in an existing method for preparing the titanium-diboride-based ceramic composite material, and belongs to the technical field of materials. The method includes the following steps that (1) TiB2 powder is evenly mixed with a carbon source and screened, and particles with the particle size ranging from 24 meshes to 60 meshes are selected as mould pressing materials; (2) the mould pressing materials are subjected to mould pressing and dried to obtain a TiB2-based biscuit; (3) the TiB2-based biscuit serves as a framework, Si is adopted as an infiltration agent for vacuum infiltration. The method is simple in step and low in temperature requirement, the titanium-diboride-based ceramic composite material high in compactness can be obtained under the condition that preparing cost is low, and the size change of a sample in the preparing process is smaller than 0.1%, so that the method belongs to net-size sintering. Besides, the method can be used for producing products in various complex shapes.