Abstract: In order to solve the problem that the existing insulation assessing methods based on polarization and depolarization current method (PDC) cannot comprehensively reflect the variation characteristics of parameters of aging cables, we proposed insulation assessing maps to show aging states of cables in multiple dimensions. An insulation assessing map includes a characteristic parameter map and a branch identification map. Water tree aging is one of the aging forms that have significant influences on cable insulation structure. After PDC tests of water tree aging cables and retired cables, the changing characteristics of insulation assessing maps were analyzed, and the abnormal characteristics of the returned cables were further analyzed by using other physical and chemical analysis methods. The results show that, with the increasing of water tree aging time, the conductivity σ of the cables does not show an obvious changing trend, while the unitized depolarizing quantity Q_n and the largest dielectric loss factor tanδ_max decrease first and then increase, which enables the area of characteristic parameter maps of water tree cables to possess the same trend. After the water tree aging of cables, the shape of branch identification maps will change significantly. Besides, the branch identification maps will move upward with the water tree aging. If some inhomogeneous structures exist in XLPE, there will be an abnormal increasing current component in depolarization currents which violates the exponential attenuation rule of depolarization currents, causing a negative fitting coefficient A_i in branch identification maps.