Abstract: A numerical simulation on the thermal process for an Si₃N₄-reaction furnace based on the software CFX was investigated. A similar flow model was used to numerically simulate the laminar flow in the furnace. The influence of some different factors such as volume quantity of N₂, anisotropic scattering and radiation properties on the temperature field and mass density of products was studied. The results showed that the temperature control on the preheating zone was important for full reaction. However, the volume quantity of N₂, i.e., inlet velocity, plays a crucial role. Anisotropic scattering influenced on the radial temperature and mass density of products. Absorption coefficient and scattering coefficient influenced little on the temperature field. The error between simulated and experimental values was less than 10%.