The embedded cocured composite material damping structure has the advantages of excellent damping properties, antiaging, nonshedding, fatigue resistance, etc. It has a broad application prospect in the field of agricultural facilities, machine tool manufacturing, aerospace, construction and other technical fields. The strain energy of the cocured composite damping structure is studied by modal strain energy method. The firstorder modal frequency and loss factor of the structure are calculated. The law of the loss factor and the firstorder modal frequency with the change of the viscoelastic damping layer thickness is obtained. The results show that when the total thickness of the thin plate is constant, the firstorder natural frequency reduces and the loss factor increases with the increase of the thickness of the damping layer. When the damping layer is thick, the firstorder natural frequency and loss factor is no longer sensitive to the change of the thickness of the damping layer. When the thickness of the composite layer is constant, the firstorder natural frequency reduces and the loss factor increases with the increase of the thickness of the damping layer. When the thickness of the damping layer is thick, the thickness of the damping layer has little effect on the firstorder natural frequency and modal loss factor. Compared with the constant thickness of the composite layer, when the total thickness of the thin plate is constant, the thicker damping layer has a smaller influence on the loss factor, which provides theoretical support for the design of lightweight damping composite materials.