The reflectance spectrum of different wBN was measured. The sample were prepared by shock-wave method and heat-treated at 100℃ and 500℃. The measurement was performed in the wavelength range of 100-240nm at the time-resolved spectroscopy station of National Synchrotron Radiation Laboratory in Hefei. The optical constants of wBN have been determined in the VUV region by applying the Kramers-Kronig relation to normal incidence reflectance data. It was found that the average value of optical band gap determined from these constants is ８．７±０．５eV. The dielectric constants, optical conductivity of wBN were also obtained. The effet of the charges of particle size and structure of the nanometer-sized wBN on the optical reflectance spectrum were further studied.