Abstract: Although macroscopic finite element simulations based on classical composite failure criteria such as the Hashin criterion can capture major damage modes—including fiber fracture, matrix cracking, and delamination—they fail to represent microscale damage mechanisms within carbon fiber reinforced polymers (CFRP), such as interfacial debonding between fibers and the matrix. To address this limitation, a multiphase micromechanical model was developed in this study, incorporating the fiber, matrix, and interfacial phases, and accounting for multiple failure mechanisms including fiber breakage, matrix failure, and interfacial debonding. The model was employed to systematically investigate the damage evolution behavior of unidirectional (UD) CFRP under representative loading conditions, including transverse tension/compression, longitudinal tension/compression, and both in-plane and out-of-plane shear. The results show that the relative errors between the simulated and experimental peak stresses and failure strains are within 5%. Moreover, the predicted crack propagation paths closely match those observed via scanning electron microscopy, thereby validating the accuracy of the proposed micromechanical framework. Based on this foundation, the model successfully captures the damage evolution of UD-CFRP under various loading scenarios, offering significant engineering value for the development of damage tolerance design criteria and structural integrity assessment methods for CFRP-based components.