Abstract: High energy and low energy ultrasonic waves were used to modify a kind of multi---walled carbon nanotubes (MWCNTs) /epoxy resin. By means of rheometer, DSC, FTIR, XPS, XRD and TEM, the physical and chemical characteristics of MWCNTs treated by ultrasonic waves with high and low energies were studied. The dispersion and compatibility of MWCNTs in epoxy resin were also analyzed. Moreover, the thermal stability and flexural property of MWCNTs/epoxy resin were measured. The experimental results show that the modified extent of MWCNTs is different with different ultrasonic wave energy. MWCNTs modified with high energy ultrasonic wave have better dispersive degree and dispersive efficiency in the resin, and the surface activity of MWCNTs is increased, which is not the case for the condition of low energy ultrasonic wave treatment. In addition, the flexural modulus and glass transition temperature of epoxy resin can be enhanced by adding a small amount of MWCNTs modified with high energy ultrasonic wave, indicating that there are strong interfaces between MWCNTs and resin matrix.