Abstract: Silicon nitride (Si₃N₄) is considered to be the best ceramic material for the comprehensive properties. High thermal conductivity and the excellent mechanical properties make it widely used as the ceramic substrate in electric vehicles and hybrid electric vehicles (EV/HEV). Sintering additives have the great influence on the sintering activity, microstructure, and the second phase composition of silicon nitride, and then affect the thermal conductivity of ceramics. Selecting the suitable sintering additives is very important for the preparation of high thermal conductivity silicon nitride ceramics. The research status of sintering additives used for the preparation of high thermal conductivity silicon nitride ceramics was summarized in this paper, the influence of sintering additives on the thermal conductivity and mechanical properties of silicon nitride ceramics was analyzed, and the future research direction and development trend of sintering additives were put forward.