SBS-modified asphalt at a concentration of 1%. The study sought to examine the impact of MWCNTs and their functional groups on asphalt’s rheological and anti-aging characteristics, alongside exploring their modification mechanisms. The findings indicated that rheological tests showed that MWCNTs/SBS composite-modified asphalt, particularly MWCNTs-OH/SBS, exhibited remarkable resistance to high-temperature deformation, a crucial characteristic for asphalt performance in hot climates. Nevertheless, it is important to note that the addition of MWCNTs led to an increase in asphalt’s creep strength and creep rate, which could potentially reduce its resistance to low-temperature cracking. However, the covalent functionalization of MWCNTs mitigated these adverse effects on low-temperature performance. Moreover, the inclusion of MWCNTs in asphalt served as a barrier, impeding the penetration of oxygen molecules and ultraviolet radiation into the asphalt matrix. This proved to be an effective means of inhibiting the aging process, a critical factor in extending the service life of asphalt pavement. Among the different formulations of MWCNTs modified asphalt, the MWCNTs-OH/SBS composite-modified asphalt exhibited notably effective anti-aging properties. Both rheological and anti-aging evaluations demonstrated that hydroxyl functional groups played a pivotal role in enhancing performance, chiefly by fostering interactions with asphalt molecules.