The invention discloses a composite magnesia carbon brick and a preparation method thereof, and belongs to the technical field of refractory materials. The composite magnesia carbon brick comprises the following raw materials: waste magnesia carbon bricks, magnesia, graphite, wax stone, slag powder, phenolic resin, epoxy resin, furan resin, polyvinylpyrrolidone, additives and the like. The preparation method comprises the following steps: (1) treatment of the waste magnesia carbon bricks: firstly, carrying out a coarse treatment and secondary treatment on the waste magnesia carbon bricks; (2)mixing: mixing the raw materials in sequence; (3) molding: pouring the mixed material into a mold, and carrying out compression molding by using a brick press to obtain a green brick; and (4) heat treatment: placing the formed green brick in a drying kiln for curing, and curing to obtain a finished product. Compared with the prior art, the prepared magnesia carbon brick has good performance advantages, and the apparent porosity, the volume density, the normal-temperature compressive strength, the normal-temperature flexural strength, the high-temperature flexural strength, the linear expansionrate and other test parameters show significant differences.