A combustion synthesis process was developed for the synthesis of magnesium silicon nitride powders in the Mg-Si-N system. The effects of ammonium halide addition and the nitrogen presssure on the phase composition and microstructure of the final product were discussed in detail. It was found that ammonium halides were helpful to enhance the nitrogen infiltration, decrease the agglomeration degree and improve the nitridation reaction. Furthermore, the nitrogen presssure greatly influenced the reaction process and the properties of the final MgSiN2 products, especially the phase composition. MgSiN2 powders with low level of impurities (MgO and free Si) could be synthesized through combustion synthesis process in the Mg-Si-N system.