Abstract: Two kinds of hBN were synthesized by using Na₂B₄O₇-NH₄Cl and Na₂B₄O₇-(NH)₂CO as the starting materials at 950, both hBN are analogous in crystallization, the average particle size was 5.6 and 1.42 μm respectively. Under high temperature and high Pressure and using Li series catalysts, cBN synthesized from the former was yellow transparent and from the latter showed black translucent. It is also found that growth stops on the surface of cBN crystals occur.The hBN obtained from the reaction of KBH₄ and NH₄Cl is amorphous with particle size of 12.43 um, and it can not transform into cBN using Li series catalysts. The synthesis mechanism of cBN was discussed.