To explore the performance evolution mechanism of SBS-modified bitumen (SMB) during construction and service, the chemical structure, molecular weight and properties of styrene–butadiene–styrene triblock copolymer (SBS) and SMB under multiple aging levels were assessed via Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC) and a dynamic shear rheometer (DSR). The results indicate that the polybutadiene segments in SBS are susceptible to oxidative degradation, and the molecular weight of SBS decreases rapidly during the aging process. The complex modulus and temperature sensitivity of SMB show relatively small changes during the early aging stage, which is mainly attributed to the impact of SBS oxidative degradation. While its temperature sensitivity decreases sharply after double PAV aging, it means the influence of asphalt aging on its performance is dominant. And there is a significant difference in the effect of aging on the creep recovery behavior of SMB under high and low shear stresses. The percentage recovery (R) of SMB decreases and then increases under low shear stress as aging progresses. While the value R of SMB increases gradually under high shear stress with the extension of aging. Meanwhile, the viscoelastic properties of SMB have gradually transformed to those of aged matrix asphalt after serious aging, which is also confirmed by the gradual destruction and degradation of the SBS cross-linked network in the binder from a fluorescence micrograph. This research will help to understand the performance failure mechanism of SMB during service, providing a theoretical reference for the selection of maintenance and renovation opportunities during the service process of SBS-modified asphalt pavement, as well as the avenue to achieve high-performance recycling.