Down-cycling flexible polyurethane foam (FPUF) waste into asphalt addresses the current shortage of effective, economic, and eco-friendly anti-aging additives and polymer disposal difficulty. In this study, anti-aging performance-oriented modification was carried out by selectively pyrolyzing and down-cycling waste FPUF. To begin with, a sustainable anti-aging fiber modifier was proposed by depolymerizing hard segments in FPUF in the temperature range of 260 to 320°C. Subsequently,The chemical, morphological, and rheological properties of pyrolyzed FPUF fiber modified asphalt (PyFMA) were evaluated to clarify anti-aging mechanisms, anti-aging behaviors, and relative competitiveness. The results showed that the proposed selective pyrolysis method was able to efficiently and conveniently produce FPUF fiber in certain temperature and duration ranges. The anti-aging enhancement of PyFMA was the result of a combination of antioxidant exchange, physical isolation, and chemical protection. Fiber dosage of FPUF played a dominant role in improving the anti-aging resistance as well as the high-temperature performance and fatigue resistance of asphalt. Quantification of anti-aging enhancement and performance improvement indicated that the FPUF fiber has competitive compared to existing synthetic, natural, and recycled additives. PyFMA composed of binder B and 24 wt% F3-T1 fiber showed the most balanced and superior performance in terms of growth ratio. In summary, the findings are beneficial for effectively and economically improving the aging resistance of asphalt and addressing the disposal difficulty of FPUF waste.