A novel design of X-ray spectrometer is implemented, using a high efficiency HOPG(highly oriented pyrolitic graphite) Bragg crystal. The spectral resolution of it can reach above 350 with energy ranging from 6.891 to 9.193 keV, theoretically. And the efficiency are 3 order of magnitude higher than the ordinary X-ray crystal spectrometer.Application of this instrument is demonstrated in high intensity laser-foil interaction experiments. It is shown that HOPG spectrometer has much lower threshold of X-ray int...