The invention discloses a method for preparing a high-purity ultrahigh-temperature ceramic target material which belongs to the technical field of ceramic target materials, and in particular provides a method for preparing high-purity zirconium/hafnium boride powder and a ceramic target material thereof. The method comprises the steps of taking high-purity Zr powder, Hf powder and high-purity B powder as raw materials, adopting a self-propagating method to prepare high-purity ZrB2 and HfB2 powder respectively and then adopting a high-temperature high-pressure hot-pressing molding process to prepare a high-purity dense zirconium/hafnium boride ultrahigh-temperature ceramic target material, wherein the relative density of the target material reaches 95 to 99 percent. Relative to the prior art, metal powder in the method is slightly excessive when the materials are mixed, so as to make up for the metal loss during self-propagating reaction and further guarantee the component unicity of products. Relative to pressureless sintering, the sintering temperature needed in the method is greatly lowered; in addition, as the hot-pressing process adopts two-stage temperature, blank is uniform in temperature field, so as to ensure that the target material with uniform density can be obtained in the late hot-pressing process.