Abstract: Comparing with optical thermography, vibrothermography(VT) is a new technique.However, the heat generation mechanism of VT has not yet come to an agreement among scholars. The VT of debondings in nonmetallic composite structures was studied focusing on viscoelastic heat.Taking the VT of debonding in aluminum-cork composite structures as an example, the temperature rise patterns on the defects were analyzed by using numerical simulation and experiment. The theoretical results are consistent with the experimental results, and it illustrates that the viscoelastic heat of the nonmetallic material is the leading factor of heat generation at debonding.The conclusion provides a theoretical basis for the VT of debondings in metal-nonmetal composite structures, and delaminations in polymer composite materials.