This paper focuses on the transverse tensile and compressive mechanical properties of T800-grade unidirectional (UD) carbon fiber-reinforced polymers (CFRPs). Firstly, transverse tensile and compressive tests were conducted on UD composite laminates, yielding corresponding stress–strain curves. The results indicated that, for tension, the transverse tensile modulus, strength, and failure strain were 8.7 GPa, 64 MPa, and 0.74%, respectively, whereas for compression, these values were 8.4 GPa, 197.1 MPa, and 3.43%, respectively. The experimental curves indicated brittle failure under tensile loadings and significant plastic failure characteristics under compressive loading for the T800-grade composite. Subsequently, fractography experiments were performed to observe the fracture morphologies, revealing that tensile fractures were through-thickness cracks perpendicular to the loading direction, while compressive fractures were at a 52° angle to the loading direction. Finally, a micromechanical finite element method (FEM) was employed to simulate the tensile and compressive failure processes of the unidirectional composite, and the tensile and compressive properties were predicted. The simulation results showed that under both tensile and compressive loadings, interfacial elements failed first, causing stress concentration and damage to nearby resin elements. The damaged resin and interfacial elements expanded and connected, leading to ultimate failure. The predicted tensile stress–strain curve exhibited linear characteristics consistent with the experimental results in most regions but showed more pronounced nonlinearity before ultimate failure. The predicted compressive stress–strain curve aligned well with the experimental results in terms of nonlinearity. The predicted elastic modulus, failure strengths, and failure strains were in good agreement with the experimental results, with differences of 1.1% (tension modulus), 3.2% (tension strength), and 13.5% (tension failure strain), and 3.6% (compression modulus), −8.5% (compression strength), and −3.8% (compression failure strain). The final failure morphologies were in good accordance with the fractography experimental observations.