Currently, only 5% of thermoset carbon fiber reinforced polymer composites (CFRPs) are recycled into lower-value secondary products. Highly efficient closed-loop recycling of both thermoset resin and carbon fiber is a major challenge. Here, we report a sustainable approach for the closed-loop recycling of the resin and fiber from CFRPs. Thiol-functionalized carbon fiber (TCF) obtained by functionalization with a thiol-ended hyperbranched polymer, and then an epoxy-ended degradable hyperbranched polymer (HT3) are used to prepare HT3/TCF composites, which show considerable acid resistance and mechanical performance. The cured composites are controllably depolymerized into monomers and oligomers with high recyclability (89%), which can be utilized to prepare HT3 and the precursor of cross-linked HT3. A total of 100% of the carbon fibers are recovered and reused to fabricate composites without deterioration of performance. The results provide a method for designing high-performance composites and a pathway for high efficiency closed-loop recycling.