Abstract: A thermodynamic analysis was performed on possible reactions of Fe₃O₄ in sediment material, intermediate product FeO, Fe, and other matters. In combination with the predominant area phase diagram of the Fe-Si system under different carbon mon-oxide partial pressures and excess carbon and silicon dioxide as well as the thermodynamic parameter state diagram of the Fe-O-N system, it is found that Fe finally exists in the form of Fe₃Si, which provides a thermodynamic theoretical basis for using sediment to synthesize O'-Sialon-SiC-Fe₃Si (Fe-Sialon) composites. These Fe-Sialon matrix composites made from sediment were prepared by carbothermal reduction-nitridation on the basis of thermodynamic analysis. X-ray diffraction and scanning electron microscopy resuhs in-dicate that plentiful O'-Sialon phase and a small quantity of SiC and Fe₃Si phases appear in samples, and the crystalline grains are fi-ber-, cotton-, or short column-shaped, which is consistent with thermodynamic analysis results.