Si_3N_4 matrix poly-phase ceramics that can be applied to super-high mach number missile radome are prepared via the reaction sintering process in this paper. Si, BN and SiO_2 powder are the main raw materials. The effects of the raw materials and the processing parameters on the mechanic properties of the material are investigated. The fracture surface of the sintered bodies is observed by scanning electron microscope (SEM). The experimental results show: the material has the highest density, highest nitri...