The present invention relates to a magnesium-calcium-based fireproof material based on microwave sintering, and a preparation method thereof. The technical scheme comprises: breaking natural dolomite, and carrying out light burning to obtain light burning dolomite; adding distilled water to the light burning dolomite, and digesting to obtain digested powder; carrying out ball milling on the digested powder, drying, and pressing to obtain a pressed billet; spreading green SiC powder at the bottom portion of a polycrystalline mullite fiber thermal insulation barrel, placing the pressed billet at the equivalent position of the polycrystalline mullite fiber thermal insulation barrel, and adding the green SiC powder until the pressed billet is completely covered; and placing the polycrystalline mullite fiber thermal insulation barrel into a microwave sintering furnace, vacuumizing the microwave sintering furnace until the vacuum degree is less than 0.5 Pa, heating to a temperature of 1200-1500 DEG C under high-purity argon at a rate of 10-60 DEG C/min, carrying out thermal insulation, and cooling along with the furnace to prepare the magnesium-calcium-based fireproof material based on microwave sintering. According to the present invention, the preparation method has advantages of rapid heating, short sintering time and low sintering temperature, and the prepared product has advantages of compact microstructure, good hydration resistance and good corrosion resistance.