Abstract: Through the method of grafting coupling agents with different chain lengths onto the surface of carbon fiber, the influence of chain lengths on interfacial performances of carbon fiber/polyarylacetylene composites was studied. Surface energy of carbon fiber before and after treatment was measured and the relation between surface energy and fiber wettability was discussed. At the same time, the interfacial adhesion was evaluated by interlaminar shear strength, and the failure mechanisms of composites were analyzed by fracture morphologies. The results indicate that with the increase in chain lengths of coupling agents on the carbon fiber surface, the interfacial adhesion of composites increases greatly. The main mechanism responsible for the improvement of interfacial adhesion is the entanglement interaction between the molecular chain of coupling agent on carbon fiber and the counterpart of polyarylacetylene resin at the interface. Moreover, the longer the chain length on the carbon fiber surface, the stronger the entanglement at the composite interface.