The invention relates to a titanium diboride ceramic powder low-temperature solid-phase synthesizing method, and belongs to the technical field of novel ceramic powder material preparation. The method comprises the following steps of: adding a small amount of polytetrafluoroethylene powder into micron-sized titanium powder and boron powder which are adopted according to a stoichiometric ratio of (1:2)-(1:2.4) as a chemical reaction accelerator; and uniformly mixing the polytetrafluoroethylene powder, the titanium powder and the boron powder at room temperature, performing cold pressing to form blanks, heating the blanks to be 530 DEG C, forming loose titanium diboride ceramic blocks through low-temperature solid-phase synthesizing reaction, and crushing the blocks to obtain the titanium diboride ceramic powder. According to the method, the micron-sized titanium powder and boron powder and the polytetrafluoroethylene powder respectively serve as raw materials and the chemical reaction accelerator to form the titanium diboride ceramic powder through low-temperature solid-phase synthesizing; and compared with the synthesizing temperature of a conventional technology, the synthesizing temperature of the titanium diboride ceramic powder solid-phase synthesizing method is reduced by 800-1500 DEG C, and the solid-phase synthesizing method is simple in technology, energy-saving, environmentally-friendly, low in cost and high in yield and purity and has a bright industrialized prospect.