The　cubic　boron　nitride　thin　film　was　deposited　with　radio　frequency　(RF)　sputtering　system　by　two-stage　deposition　process　method.　The　content　of　c-BN　was　characterized　by　Fourier　transform　infrared　(FTIR)　sprectroscopy.　The　transmitted　spectrum　and　reflectance　spectrum　was　measured　by　UV　spectrophotometer.　The　curve　of　absorption　coefficient　α　vs　hv　and　optical　band　gap　Eg　was　calculated,　the　Eg　is　almost　equal　to　the　results　from　the　empirical　formula.