Abstract: The Si₃N₄-SiC-TiN multiphase ceramic was synthesized f rom TiSi₂ and SiC powders by self-propagatinghigh-temperature synthesis in which SiC is acting as a diluent . The effect of nit rogen pressure on the conversiondegree of the reactant was calculated in theory , and combustion synthesis was carried out under nit rogen pressuresof 50 , 100 and 150 MPa , respectively. The result s show that the green part s of 50 vol % porosity are well nit rifiedunder the three pressures , while those of 40 vol % porosity can not be nit rified completely in which agglomerate Si isfound when they were synthesized under lower pressure. However , there is no Si detected in the final product s madeby 40 vol % porosity part s under 150 MPa nit rogen pressure. Accordingly , the high nit rogen pressure is of advantage to the infilt ration of nit rogen and the increase of conversion degree.