Abstract: The optimal parameter of the ultrasonic treatment is studied, emphasizing on the research of the effect of the ultrasonic treatment on the interfacial performance of RTM composites. In order to increase the resin impregnation for fiber mats the ultrasonic technique was used. The results show that the resin viscidities are decreased and its flow velocities at the flow front are increased when the ultrasonic irradiates on the mold during the process of RTM. Furthermore, air traps are very difficult to be formatted, and the impregnation is improved considerably. Hence, interfacial performances of the composites are enhanced.