We have been developing X-ray mirrors for X-ray telescope using a ion-beam sputtering system. X-rays can be reflected by two processes, one is total reflection, and another is Bragg reflection. Total reflection is used for previous telescope below 10 keV. Its reflectivity determined by the optical constant. We suggests composite-layer mirror for soft X-ray optics, which has consists some different materials and optical constant has structure to the depth direction. The penetration depth of X-ray depends on the X-ray energy, so effective optical constant changes with X-ray energy. The depth graded multilayer, called "supermirror" was applied to the soft X-ray region. We designed nickelcarbon supermirror to obtain high reflectivity below 10 keV.