This paper proposes a segmented wave speed estimation method using attenuation constants to address uneven wave velocity distribution in cross-linked polyethylene cables caused by segmental aging in urban power grids. Traditional traveling wave methods, constrained by uniform wave speed assumptions, struggle to reflect actual cable conditions and compromise fault location accuracy. Our solution establishes a frequency-dependent coupling model between attenuation constants and phase velocity to resolve parameter decoupling challenges. The methodology integrates frequency-domain reflection for acquiring cable transfer function’s amplitude-frequency characteristics, applies singular value decomposition (SVD) denoising to enhance signal stability, and employs the Prony algorithm to fit exponential decay terms, enabling precise sectional wave speed estimation. Simulation results demonstrate effective extraction of average wave speeds across three 1500 m cable segments, validating the method’s capability in assessing cables with varying aging degrees. This research advances cable aging monitoring and fault localization strategies, supporting improved grid operation reliability and maintenance efficiency.