The invention relates to a fired magnesia-calcium brick and a preparation method thereof. According to the technical scheme, 60-65 % of electrically smelted dolomite sand particles are used as aggregates by weight, and 10-15 % of fine electrically smelted dolomite sand powder, 10-15 % of fine electrically smelted magnesia sand powder, 5-8 % of Cr7C3 micro-powder, 3-6 % of light and fine fired dolomite clinker powder and 1-4 % of cobalt oxide micro-powder as substrate materials by weight; firstly, the substrate materials are mixed evenly, then the evenly mixed substrate materials are added to the aggregates, and even mixing is performed; secondly, liquid paraffin accounting for 5-6% of the weight sum of the substrate materials and the aggregates is additionally added, and even mixing and mechanical pressing formation are performed; finally, the mixture is arranged in a muffle furnace, heating is performed to reach 1600-1600 DEG C at the heating rate of 3-5 DEG C/min, heat preservation is performed for 3-5 hours, and cooling is performed with the furnace to prepare the fired magnesia-calcium brick. The fired magnesia-calcium brick has the advantages of being simple in process and low in cost. The prepared fired magnesia-calcium brick has good sintering performance and excellent anti-hydrating capacity.