The main objective of this paper is to evaluate the effects of asphalt concrete types on the microstructural characteristics at high-temperature.Suspend-dense structure and Skeleton-dense structure were selected to investigate the deformation of pavement at meso-scale.The internal microstructures of typical asphalt concretes,AC,SUP and SMA,were scanned by X-ray CT device,and microstructural changes before and after high-temperature damage were researched by digital image processing.Adaptive threshold segmentation algorithm(ATSA) based on image radius was developed and utilized to obtain the binary images of aggregates,air-voids and asphalt mastic.Then the shape and distribution of air-voids and aggregates were analyzed.The results show that the ATSA can distinguish the target and background effectively.Gradation and coarse aggregate size of asphalt mixtures have an obvious influence on the distribution of air-voids.The movements of aggregate particles are complex and aggregates with elliptic sharp show great rotation.The effect of gradation on microstructure during high-temperature damage promotes the research about the failure mechanism of asphalt concrete pavement.