Boron nitride (BN) crystals were synthesized from aqueous solutions by reaction coupling effect. The effects of white phosphor (P), ammonium chloride (NH4C1) and the reaction temperature on the yield and crystalline perfectness of BN crystals have been explored. The results showed that, the existence of P in the reaction mixture significantly increased the yield and perfectness of the BN crystals. BN crystals grew larger and more perfect when the temperature increased from 300℃ to 550℃.The yield and perfectness of BN can also be improved greatly by adding NH4C1 to the reaction mixture. The samples were characterized by powder X-ray diffraction (XRD), Fourier transformation infrared absorption spectrum (FTIR), Transmission electron spectroscopy (TEM) and Selective area electron diffraction (SAED).