By introducing multiple defect layers in one dimensional (1D) photonic crystal (PC), the broadband slow light with low dispersion is obtained. The slow light pass band is smoothed by adjusting the spacing and the number of cavities. In the optimized structure, the bandwidth is 8.556 1 nm with flatness below 8.805 2×10_-4, the group velocity is in the range from 0.029c to 0.042 4c, and the group velocity dispersion (GVD) parameter D is in the range from -14.410 3 ps/(mm·nm) to 15.124 ps/(mm·nm). Moreover, by material optimization, the slow light properties can be improved further. With suitable materials, the slow light pass band can be broadened to 20.057 8 nm with flatness of 5.4×10_-3, and the GVD parameter D decreases to the range from -4.657 8 ps/(mm·nm) to 4.790 4 ps/(mm·nm).