The shape characterization and spatial distribution of aggregate,mastic and air void phases for asphalt mixture were analyzed.Three air void percentage asphalt mixtures,4%,7% and 8%,respectively,were cut into cross sections and polished.X-ray scanning microscope was used to capture aggregate,mastic,air void phase by the image.The average of polygon diameter was chosen as a threshold to determine which aggregates would be retained on a given sieve.The aggregate morphological image from scanned image was utilized by digital image processing method to calculate the gradation of aggregate and simulate the real gradation.Analysis result shows that the air void of asphalt mixture has influence on the correlation between calculation gradation and actual gradation.When comparing 4.75 mm sieve size of 4%,7% and 8% air void asphalt mixtures,7% air void asphalt mixture has 55% higher than actual size gradation,8% air void asphalt mixture has 8% higher than actual size gradation,and 4% air void asphalt mixture has 3.71% lower than actual size gradation.4% air void asphalt mixture has the best correlation between calculation gradation and actual gradation comparing to other specimens.The air void percentage of asphalt mixture has no obvious influence on the air void orientation,and three asphalt mixtures show the similar air orientation along the same direction. The shape characterization and spatial distribution of aggregate, mastic and air void phases for asphalt mixture were analyzed. Three air void percentage asphalt mixtures, 4%, 7% and 8%, respectively, were cut into cross sections and polished. X- ray scanning microscope was used to capture aggregate, mastic, air void phase by the image the average of polygon diameter was chosen as a threshold to determine which aggregates would be retained on a given sieve. aggregate morphological image from scanned image was utilized by digital image processing method to calculate the gradation of aggregate and simulate the real gradation. Analysis result shows that the air void of asphalt mixture has influence on the correlation between calculation gradation and actual gradation .When comparing 4.75 mm sieve size of 4%, 7% and 8 % air void asphalt mixtures, 7% air void asphalt mixture has 55% higher than actual size gradation, 8% air void asphalt mixture has 8% higher than actual size gradation, and 4% air void as phalt mixture has 3.71% lower than actual size gradation.4% air void asphalt mixture has the best correlation between calculation gradation and actual gradation comparing to other specimens. air void percentage of asphalt mixture has no obvious influence on the air void orientation, and three asphalt mixtures show the similar air orientation along the same direction.