ZrB2 in MgO-C composite materials obtained by both microwave sintering synthesis and in-situ reaction at lower temperature was investigated. The test result shows that 66.67% of reactant changed into ZrB2, and the other form Al2O3, which could optimize the properties of carbon-containing materials. Therefore, the method of in-situ synthesizing ZrB2 acting as antioxidant in carbon-containing materials is considered as one of best ways to reduce the cost and ZrB2 as refractories is used on a large-scale.