The authors present the results of investigations on combustion synthesis (SHS) in the Si-C-N system in order to prepare composite Si3N4-SiC powders. A new approach by a realisation of self-sustaining combustion in the Si-C-N system without an inert dilution is reported. This makes possible the preparation of a full range of carbide-nitride composite powders, including pure SIC and Si3N4 powders. An analysis of the SHS process in the Si-C-N system is based on temperature profiles of a propagated heat wave. The temperature phenomena are correlated with the product phase composition, specific surface area and morphology. The simultaneous reactions occurring during SHS are identified, namely : nitridation of silicon, direct reaction between silicon and carbon and carbothermal reduction of silicon nitride. A complex mechanism of SHS in the Si-C-N system is next discussed.