With the rise of the third-generation wide-bandgap semiconductors represented by SiC and GaN, power electronic devices are developing rapidly towards high output power and high power density, putting forward higher performance requirements on ceramic substrate materials used for power module packaging. The conventional Al₂O₃ and AlN ceramics are inadequate for the new generation of power module packaging applications due to low thermal conductivity or poor mechanical properties. In comparison, the newly developed Si₃N₄ ceramics have become the most potential insulating heat dissipation substrate materials due to its excellent mechanical properties and high thermal conductivity. In recent years, researchers have made a series of breakthroughs in the preparation of high strength and high thermal conductivity Si₃N₄ ceramics by screening effective sintering additive systems and optimizing the sintering processes. Meanwhile, as the advancement of the engineering application of coppered Si₃N₄ ceramic substrate, the evaluation of its mechanical, thermal, and electrical properties has become a research hotspot. Starting from the factors affecting thermal conductivity of Si₃N₄ ceramics, this article reviews the domestic and international research work focused on sintering aids selection and sintering processes improvement to enhance the thermal conductivity of Si₃N₄ ceramics. In addition, the latest progress in the dielectric breakdown strength of Si₃N₄ ceramic substrates and the evaluation of properties after being coppered are also systematically summarized and introduced. Based on above progresses and faced challengies, the future development direction of high strength and high thermal conductivity Si₃N₄ ceramic substrates is prospected.