Recently growing interest has been focused on photopolymers for their advantages in holographic storage memory. For large memory capacity, one of the basic requirements is that the recording material thickness must be 500 μm or thicker. Nevertheless, the attenuation of the light in depth due to absorption limits the effective optical thickness inside material, which reduces the holographic performance of photopolymer. In this work, the influence of the effective optical thickness of photopolymer on its holographic characteristic was studied theoretically and experimentally. To overcome the attenuation of gratings for a better uniformity, a technique of multi-layer was introduced, by adjusting concentrations of dye along the depth of photopolymer to compensate the attenuation of recording light due to absorption. Multi-layer photopolymers based on PVA/AA with thicknesses more than 500 μm were designed, fabricated, and characterized experimentally, exhibiting better Bragg selectivity. The attenuation of gratings was suppressed, and the effective optical thickness was enhanced. More holograms were stored in multi-layer material by angular multiplexing, and the cumulative grating strength was enhanced, leading towards larger holographic storage capacity. Also, with the theoretical simulation on the distributions of the gratings inside the material, the improvement of multi-layer technique in holographic performance is shown.