Abstract: One of the main factors to influence the interfacial properties of composites is the surface characteristics of the aramid fiber. Ultrasound is used to treat the surface of the aramid fiber and the change of surface structure of the aramid fiber under the ultrasonic treatment is investigated in this paper. The results show that the content of polar group and the specific surface area increase so as to improve the wettability between the aramid fiber and epoxy resin.