Abstract: Two methods were used to characterized the kinetics of SHS Si₃N₄ during the process of Si combustion under high pressure of nitrogen. Activation energy of 75.4 KJ·mol^-1 was calculated by using method which was named “wave velocity method” compar-ing to the calculated value of 54.3 kJ·mol^-1 by using the other method which was named “reaction rate method”. The discrepancy between the values calculated with these two different methods account for the “after-burn nitridation” process. As the diluent of Si₃N₄ added increased. The maximum combustion temperature decreased and the thermal conductivity increased smoothly. While the gas transport agent was added, thepropagating velocity of combustion wave was decreased and the activation energy was increased.