In this paper the photoelectric characteristics of the three channel bulk charge coupled device (BCCD) are simulated in the region of X ray.The results show that the silicon three channel BCCD can not realize multi spectral imaging in the region of X ray.Based on the result of theoretical research the absorption coefficient curve of a substrate material has be found,which ensure the three channel BCCD work in the region of X ray.The three channel BCCD made by the new material will have three maxim positions of the spectral photosensitivity at 1.8 keV,1.2 keV and 0.6 keV,respectively.