The triethanolamine borate was synthesized by triethanolamine reacting with boric acid and using toluene as water carrying agent. The h-BN particles were prepared by sintering triethanolamine borate as precursor in ammonia gas atmosphere. The precursor and product were respectively characterized by IR, XRD, SEM and NMR analyses. The results indicated that the precursor is treated at 1200℃ for 4h to receive high purity and good crystals of h-BN particles with a average particle size of 20μm. After high-temperature refining of h-BN particles with high crystallinity and compactness, the particle size can reach more than 30μm and 98.5% purity can be obtained.