Abstract: In this paper, the effectiveness of ultra-low frequency dielectric loss in evaluating the insulation aging state of XLPE cables is described. The ultra-low frequency dielectric loss of 21 10kV cables in Tianjin area was measured. On the basis of the analysis of the relationship between the ultra-low frequency dielectric loss and the aging of insulated water branch aging, according the International Society of Electrical Engineers IEEE400.2-2013 IEEE Guide for Field Testing of Shielded Power Cable Systems Using Very Low Frequency(VLF)(less than 1Hz), the test date are analyzed. The results are shown that 9 of the 21 cables are in a state of need for further test or maintenance. The longer the service time, the more cable failures, the more serious the aging degree. The ultra-low frequency dielectric loss can effectively evaluate the insulation aging state of XLPE cables, which is of great significance for guiding the reconstruction of the distribution network cable in Tianjin.