The invention relates to a method for preparing high-purity magnesite clinker. The method is characterized in that the preparation method comprises that: according to weight proportion of 4:1, magnesite and graphite powder are mixed and roasted to form soft burnt magnesia powder; according to weight proportion of 5:1, the soft burnt magnesia powder with magnesium content of 95 percent and rare-earth magnesium are evenly mixed and pressed to form a pellet with diameter of between 40 and 50 mm; the volume density of the pellet is 2.5; and the pellet is sintered at high temperature to form the high-purity magnesite clinker. By the process, the high-purity magnesite clinker with purity of more than 99.8 percent can be obtained. The method for preparing the high-purity magnesite clinker has the advantages of improving the magnesium content of high and medium-grade magnesite clinker to 99.8 percent and simultaneously improving the volume density of the magnesite clinker to 3.5 above.