Abstract: Vibro-acoustic modulation technique (VAM) is a novel nonlinear ultrasonic method. The principle of VAM was briefly introduced, and then VAM with sine wave excitation and swept probing excitation was utilized to detect the fillet weld of small diameter nozzle stubs sample. It was found that the modulation intensity of defect sample was larger than reference sample, this difference would be much larger in some special high frequency range, which would be more beneficial to distinguish the weld quality. And the proper high frequency range can be quickly obtained by the swept probing excitation technique. Compared with the ultrasonic C-scan results, it was indicated that the VAM technique can be used to evaluate the quality of the fillet weld, however, further work is required to locate and quantitatively detect the damage.