By logically superimposing three base one dimensional (1D) photonic crystals, the broadband slow light with low dispersion is obtained. The slow light pass band is smoothed by adjusting the period ratio of three base structures, period number of new photonic crystal (PC) and the filling factor. In the optimized structure, the minimum of transmission (T) arrives at 0.5902, the full width half maximum (FWHM) is 55nm, the group velocity is in the range from 0.08326c to 0.2912c, and the group velocity dispersion (GVD) parameter D maximum is 14.65 ps2/nm·mm. Moreover, by material optimization, adjusting the refractive index of na and nb, the slow light properties can be improved further. With suitable materials, the T minimum increases to 0.6485, the group velocity decreases to the range from 0.08014c to 0.2592c, and GVD parameter D maximum decreases to 13.98 ps2/nm·mm with FWHM 52nm.