To address the prolonged high-temperature thermal exposure of hypersonic vehicles, this study examines the mechanical property evolution of TC4 titanium alloy after thermal exposure at 600 °C for 0–800 h. Experimental results show that elastic moduli remain largely stable, while strength and tensile ductility degrade progressively with prolonged exposure. Scanning electron microscopy (SEM) of fracture surfaces reveals that thermal exposure reduces the effective load-bearing cross-sectional area and induces surface-initiated damage, thereby increasing the likelihood of inward fracture propagation. Microstructural analysis via comparative metallography identifies grain growth and an increased volume fraction of primary α-phase as the primary mechanisms driving property deterioration. A validated mathematical model accurately predicts strength degradation kinetics with a maximum error of 4.5%, closely aligning with experimental data and confirming its reliability for predicting high-temperature mechanical degradation. This study provides critical insights for optimizing material selection and failure prediction in hypersonic vehicle design.