Abstract: XLPE distribution cables have large spatial spans and complex operating environments, after long-term operation, they are prone to segmented aging, thus, it is of vital importance to locate cable defects accurately. Existing studies have established diagnostic functions based on broadband impedance spectrum (BIS), which could locate impedance discontinuities in cables, but could not distinguish between aging segments and concentration defects in cables. In this paper, the limitations of the existing diagnostic functions used to identify cable defects were analyzed through simulation, and a new diagnostic function was built, then a method for distinguishing and locating thermal aging cable segments and concentration defects based on the waveform characteristics of the diagnostic function was proposed. Meanwhile, the cause of the characteristic peak waveform was revealed by theoretical analysis. Finally, a 60m XLPE cable model with defects was prepared in the laboratory and the effectiveness of the proposed method was verified by experiments. Experimental results show that the method proposed in this paper can effectively identify and locate the aging cable segments and concentration defects. This research has wide application prospect in condition assessment and condition-based maintenance of distribution cables.