Considering the effect of higher-order shear deformation in thick damping layer, a new model called “continuous stress model” is proposed for the ACLD structures. Based on the Reddy’s simplified higher-order shear theory, a three-order displacement field is applied to the damping layer. So both the displacements and shear stresses are ensured to be continuous at the interfaces of three different layers. And the novel spectral finite element method (SFEM) is used to model a fully ACLD beam and comparisons are made between the new model and the traditional Mead-Markus model. It can be seen that the continuous stress model is better than the Mead-Markus model on predictions of natural frequencies and modal loss factors.