In this study, the synthesis is feasibility and formulation design of HfN composite lanthanum silicate ceramics were explored. The feasibility of HfN synthesis by ternary reaction of HfO₂-Si₃N₄-La₂O₃ system was verified by experiments, and the relationship between reaction pathway of HfO₂-Si₃N₄ binary system and Hf-Si-La-O-N was studied. Considering that the lanthanum silicate salt in the reaction of HfO₂-SiO₂-La₂O₃ ternary system was contained in the Si₃N₄-SiO₂-La₂O₃ system, lanthanum silicate was extended to the HfO₂-Si₃N₄-La₂O₃-SiO₂-HfN (Hf-Si-La-O-N) system, which clarified the coexistence of HfN and the lanthanum salt phases in the system. Experimental phase diagrams of HfO₂-SiO₂-La₂O₃ ternary system and Hf-Si-La-O-N system at 1500 ℃ were proposed. The results show that intermediate product Hf₇O₈N₄ formed in the synthesis of HfN at high temperature in HfO₂-Si₃N₄ binary system. Introduction of La₂O₃ promoted the system to generate HfN which was beneficial to reduce the burning loss rate of ceramics. There existed HfN and La_4.67Si₃O₁₃, La₅Si₃NO₁₂, LaSiNO₂, La₄Si₂N₂O₇, La₂Hf₂O₇ five lanthanum salt phases in the Hf-Si-La-O-N system.