Abstract: Experimental and numerical studies on the bearing response of single-lap, countersunk composite joints which were designed according to ASTM 5961 under various bolt preload were presented. The specimens were manufactured from carbon fiber/epoxy unitapes with quasi-isotropic lay-ups. To obtain a more accurate hole strain, 2D digital image correlation (DIC) measurement technique was used. Three-dimensional finite element model was constructed using ABAQUS/standard and validated by comparing to the experiment. The validated model was used to provide a detailed stress analysis around the hole boundary considering various bolt preload and friction conditions. The results show that countersunk hole is the region where the severest damage occurs, and bolt preload could significantly improve the 2% hole deformation bearing strength but only slightly increase the ultimate bearing strength. Through stress analysis, increasing either bolt preload or friction between laminates are found to have an active effect on relieving stress concentration, and will make a better bearing performance of single-lap, single-bolt, countersunk composite joints.