The invention discloses a method for preparing chromium-containing magnesia from magnesite light burning powder. The method is characterized by comprising the following steps: pretreating light burning powder at the temperature of 850 DEG C or higher to obtain pretreated light burning powder; hydrating the pretreated light burning powder with water to obtain ore pulp, adding a magnesium source tothe ore pulp, and removing calcium to obtain calcium-free ore pulp; adding a Cr source to the calcium-free ore pulp; performing chromium precipitation reaction, and performing solid-liquid separationto obtain a precursor; and sintering the precursor to obtain the chromium-containing magnesia. Through a lot of researches, inventors find that the light burning powder is preheated to the set temperature so as to be pretreated, then hydration is preformed, the magnesium source (providing Mg<2+>) is added to the ore pulp obtained by hydration, calcium hydroxide impurities are converted through theprecipitation conversion mechanism, and then, the Cr source (providing Cr<3+>) is added; and through the precipitation conversion mechanism, formed chromium hydroxide is avoided from falling and separating from the surface of a magnesium oxide source, and the uniform dispersity of the chromium hydroxide in the precursor is greatly improved, thereby obtaining the chromium-containing magnesia withexcellent performance.