In order to study the influence of void fraction and density of asphalt mixture on the performance of pavement overlays, CT scan was adopted to drill core samples to obtain 2D slices combining actual engineering. The distribution of substances in each layer of the pavement was analyzed qualitatively. The results show that modified asphalt SMA-13 layer has higher cohesive force and internal friction force. There is squeezing phenomenon at the position near the joint of modified asphalt SMA-13 layer and modified asphalt AC-20C layer, 5 mm far away from modified asphalt AC-20C layer. When the particle density of modified asphalt AC-20C layer meets the requirements, the fine aggregate content of the mixture is increased and the coarse aggregate content is decreased compared with modified asphalt SMA-13 layer. The density and void fraction of modified asphalt AC-20C layer are increased greatly compared with modified asphalt SMA-13 layer, and the void distribution is more uniform.The void fraction of modified asphalt AC-20C layer is increased greatly compared with that of the joint, but the void presents the same shape and distribution. The waterproof anti-cracking bonding layer has low void fraction and compact structure. The research results can provide some reference for material selection in highway reconstruction and extension projects.