Abstract: The surface of polyacrylonitrile(PAN)-based carbon fibre was modified by high energy laser beam. SEM, EDS, FTIR, XRD, and tensile testing machine were used to characterize the morphology, change of composition, phase structure, and mechanical properties of carbon fibre before and after modification. The effect of laser beam on changes of carbon fibre microstructure was systematically studied to explore the mechanisms of laser beam on carbon fibre. The results show that surface roughness, specific surface area and infiltration of carbon fibre are improved after laser surface modification. When the power is higher, scanning speed becomes lower, carbon fibre wettability exhibits better. There are no changes in chemical composition, microstructure and type of functional groups of the modified carbon fibre. The type of functional group of modified carbon fibre is not changed, which indicates that process of laser modification is mainly based on physical process. The laser modification does not change the microstructure of carbon fiber. A slight decrease in microcrystalline size is beneficial to improve to the interfacial adhesion properties between carbon fiber and epoxy resin. The tensile strength, impact strength of modified carbon fibre/epoxy resin composites are also improved. When the mass fraction of carbon fibre is 0.2wt% and modified power is 150 W, the tensile strength of carbon fibre/epoxy resin composite increases by 59%, and the impact strength increases by 52%.