To study the characteristics of X-ray backlighter generated by laser irradiating a foil, a backlit elliptically bent crystal spectrometer is developed based on the ellipse focusing theory. The elliptical mica (002) crystal is employed with 1350 mm focal length, 0.9586 eccentricity and 50°~67° Bragg angle. The laser is of 30° incident angle and perpendicular to long axis of elliptical mica. Diffraction detecting angle is 100°~120° and the wavelength is 0.14~0.16 nm. X-ray CCD is taken as the signal detector. The experiment is carried out on SGⅡ where the 7# and 8# lasers irradiate 10 μm Cu foil simultaneously. CCD obtains the X-ray spectral information of the similar helium and Kα spectra of Cu plasma X-ray. It is demonstrated by spectrum unfolding that spectral lines have obvious basement, and the spectral resolution is over 700 after difference denoising with the least square method.