Si₃N₄ ceramics with high thermal conductivity and high strength were fabricated through gas pressure sintering at 1 MPa N₂ and 1850 ℃ , holding for 4 h in this study. Effects of doping methods (coating and traditional ballmilling) and sintering additive content on the phase composition, relative density, microstructure, mechanical property and thermal conductivity of the as-prepared Si₃N₄ ceramics were systematically studied. The results show that increasing the sintering additive content enhances the second-phase crystallinity, relative density, mechanical property, and thermal conductivity of the Si₃N₄ ceramics. Compared with the traditional ball-milling method introducing sintering additives, the coating method is more favorable to improving the dispersion uniformity of sintering additive, enabling Si₃N₄ ceramics to form a continuous network liquid phase with sintering additive mass fraction of merely 3%, thereby promoting the densification, improving microstructure uniformity, and ultimately enhancing the mechanical property and thermal conductivity of Si₃N₄ ceramics. The sample prepared using the coating method with sintering additive mass fraction of 5% achieved a thermal conductivity of 76.07 W·m^–1·K^–1, fracture toughness of 8.39 MPa·m^1/2 and bending strength of 922.41 MPa, and showing a 13% increase in bending strength compared with the ball-milled sample.