Constrained layer damping treatments such as sandwich beams are considered as the most efficient way of introducing vibration damping into a structure. The dynamic mechanical properties and damping behavior of a laminated sandwich composite beam inserted with a viscoelastic layer is investigated. A quantitative analysis of damping in the sandwich laminated composite beam has been conducted through the theoretical and experimental method. Traditional epoxy and new kind of polyurea viscoelastic layer are selected to analyze the damping properties. Results showed that the polyurea viscoelastic layer had good dumping capability. The effects of temperature, frequency of viscoelastic layer on vibration damping characteristics arc also discussed. They also demonstrate the great capability of laminated sandwich composites with embedded viscoelastic layer to considerably enhance structural damping.