Abstract: The dynamic compressive properties of unidirectional composites made of TG800 carbon fibers and an epoxy resin were tested by the split Hopkinson pressure bar method. Effects of the fiber diameter and surface treatment by anodic oxidation on the dynamic compressive properties and fracture failure modes of the composites were investigated by SEM combined with numerical simulation. Results indicated that the TG800/epoxy resin composites had a brittle fracture behavior and strength increased as strain rate, interface strength or fiber diameter increased during dynamic compressive property testing. With strong interfacial bonding enabled by the surface treatment, when the fiber diameter was increased from 5 to 6 μm the dynamic compressive strength increased by about 18% and the primary failure mode changed from fiber breakage and debonding between fiber and resin to plastic deformation of the resin and debonding between fiber and resin. When 5.4 μm diameter fibers were used, a comparison of weak (not oxidized) versus strong interfacial bonding, showed that the dynamic compressive strength for the former was about 6% lower, and the failure mode of the latter was fiber breakage, plastic deformation of the resin, and debonding between fiber while the former was only debonding between fiber and resin.