Using flashing combustion synthesized Si 3 N 4 and silica fume as raw materials, the effects of firing temperature (1300°C, 1400°C, 1500°C, and 1600°C) and duration (3h, 6h, and 9h) on the synthesis of Si 2 N 2 O were studied. The results show that the main mechanism of the reaction is Si 3 N 4 and silica fume react to form Si 2 N 2 O through solid-solid reaction or solid-liquid reaction. After heat treatment at 1300°C, there is a small amount of melting liquid in the system, with a trace of Si 2 N 2 O formed. After heat treatment at 1400°C, 1500°C, and 1600°C, there is a large amount of melting liquid in the system, accelerating the formation of Si 2 N 2 O slightly. The duration has very little effect on the synthesis reaction. When Si 2 N 2 O forms, the oxygen content in the melting liquid decreases, viscosity of the liquid increases, the diffusion of ions in the melting liquid slows, hindering the continuous crystallization of Si 2 N 2 O. Thus, a fusing agent or hot pressing is required to introduce more low viscosity liquid for the continuous crystallization of Si 2 N 2 O. In addition, silica fume crystallizes obviously at 1300°C and 1400°C.