The gaseous disks surrounding massive black holes are widely believed to power a range of active galactic nucleus (AGN) phenomena. However, direct and accurate measurements of the disk density structure remain challenging with current electromagnetic observational facilities. For the first time, we propose that an inspiralling stellar-mass binary black hole embedded in an AGN disk can serve as a precise probe for reconstructing the entire density profile. When the binary’s barycenter follows an eccentric orbit around the central supermassive black hole, space-borne gravitational-wave detectors — through multi-year monitoring of the gravitational waveform evolution — can measure with high accuracy both the density and the radial profile of the surrounding disk. Our results indicate that the inferred density profile can be constrained to within 2 × 10^−11 g/cm^3. This approach opens a new window into the innermost regions of AGNs, allowing the reconstruction of disk gas density distributions ρ(r) from environmentally imprinted modulations in gravitational-wave signals.
