Abstract: The characteristics of vibration and sound radiation from a double shell with the outer shell coated with viscoelastic layer are systematically studied. The shell's motion function is expressed by the classical Flugge operator and the layer's motion function is described by three-dimensional Navier equations whose displacement solutions are expressed by Taylor expansion along the layer thickness. The continuity conditions of displacement and stress between the shell and the layers are used in obtaining the vibration equations. The effects of layer thickness, modulus of elasticity, the loss factor, and the hydro-compressibility on the structural acoustic characteristic are discussed in detail. It showed that the higher the modulus of elasticity is, or the thinner the thickness of layer is, or the smaller the loss factor is, the higher the sound radiation power is. The influence of the layer mass on the sound radiation must be taken into account at higher frequency. It is favor of noise reduction to choose lower density layer.