In order to investigate the effect of the catalyst loading mode on the mechanical properties of Si3N4 composite MgO-C refractories prepared by nitridation, fused magnesia, flake graphite, silicon powder, and phenolic resin were used as the main raw materials, and ferric nitrate as the catalyst to prepare refractories by nitriding at 1 350 °C. The effects of different catalyst supports (silicon powder, silicon powder + phenolic resin) on the formation of Si3N4 in MgO-C refractories and the properties of refractories were studied. The results show that the silicon powder + resin catalyst support promotes the participation of α-Si3N4 in the reaction to generate β-Si3N4 and MgSiN2,and generates more SiC. However, this loading mode causes more gas to escape from the refractories and loosens the material structure, which reduces the mechanical properties. On the contrary, MgO-C refractories prepared by nitridation with silicon powder-supported catalysts under the same conditions show higher density and better mechanical properties.