The development of nanomaterials as highly efficient contrast agents for tumor computed tomography (CT) imaging still remains a huge challenge. In this study, a novel and facile approach to fabricate unimolecular micelles-stablized gold nanoparticles (AuNPs) without external reductant for in vitro targeted CT imaging was described. Amphiphilic 21-arm star-like polymers beta-cyclodextrin-g-{poly(2-(dimethylamino)ethyl methacrylate)-poly(2-hydroxyethyl methacrylate)-poly[poly(ethylene glycol) methyl ether methacrylate]) [beta-CD-g-(PDMA-b-PHEMA-b-PPEGMA)] was firstly synthesized and proved to form unimolecular core-middle layer-shell-type micelles in water through experimental and computer simulation results. Taking advantage of the reducing groups of PDMA block, AuNPs were decorated in the micellar PDMA block because of the in situ reduction of gold ions, which were absorbed by the PDMA chains in the core layer with a narrow nanoparticle size distribution. This strategy could prevent aggregation of AuNPs, which were capable of being employing as a highly effective probe for specific CT imaging in vitro. Importantly, the beta-CD-g-(PDMA-b-PHEMA-b-PPEGMA)/AuNPs incubated with HepG2 cells, displayed more intense X-ray attenuation property (>37%) than conventional iodine-based CT imaging agent (Omnipaque) and also possessed a satisfying cytocompatibility in the given concentration range.