A new composite viscous damping material is developed to reduce the vibration and noise of car body. To analyze the mechanism of vibration and energy dissipation of the new type of viscous damping material on car body, the essay, based on the studies of the classic free damping layer and constrained layer damping, a composite damping layer with elastic constraints, composite shear, and its bending energy dissipation mechanisms is proposed.. Based on the displacement continuous relations of layers and thin plate theory, the displacement and strain energy equationsare established. According tothe boundary conditions of local damping equipped and four edges simply supported, the composite damping plate motion differential equation and the eigenvalue equation of the vibration frequencyare deduced by combined with the assumption mode method.The natural frequency and the loss factor of the composite damping plate are also obtained.The composite damping layer can be used to study the different parameter characteristics of single-phase materials and the performance comparison of multiphase materials. In addition, the elastic layer moves up, the vibration damping performance is better.The derivation of the composite energy dissipation mechanism formula also provides a theoretical basis for its applications in automobiles.