A novel carbon fiber reinforced viscoelastic composite (CFR-VEC) layer has been developed for passive damping in structural vibration control especially in aerospace industries, via constrained layer damping (CLD) treatment. Unlike conventional monolithic viscoelastic material (VEM) layers, the CFR-VEC layer reinforced unidirectional carbon fibers into the constrained viscoelastic layers. This innovative CFR-VEC layer is incorporated into the core layer of a sandwich beam structure, replacing the traditional monolithic viscoelastic layer, to assess its damping performance. In the results and discussion section, the variations in material properties of CFR-VEC with different volume fractions and the relevant frequency range are analyzed. The findings indicate that the shear stiffness coefficient increases with higher volume fractions while maintaining the shear damping coefficient, consequently resulting in greater dissipation energy within the sandwich beam structure. Based on the concept of linear viscoelasticity, the dissipated energy is quantified as the product of the storage modulus and the modal loss factor. Within the passive constrained layer damping (PCLD) treatment of the sandwich beam, the dissipated energy in shear form plays a pivotal role in attenuating vibrations across the structure. Thus, it is evident that the incorporation of carbon fiber into the viscoelastic material significantly enhances passive damping within the sandwich beam, contributing to its vibration attenuation properties.