Abstract: Non-metallic outer sheath of single-core high voltage cables mainly serves the purposes of insulation isolation and mechanical protection, and its electrical performance directly affects operational safety of the cables. As the damage of outer sheath can lead to multiple grounding points of metal sheath and cause circulating current losses, it is necessary to verify its insulation reliability through withstand voltage tests. In the paper, technical characteristics of AC and DC withstand voltage tests based on cable construction principles and relevant standard requirements were compared, and differences in detection efficiency between the two methods were clarified. Insulation requirements and induced voltage carrying characteristics of non-metallic outer sheath were analyzed in accordance with GB/T 11017.1—2024, GB/T 18890.1—2015 and GB/T 22078.1—2008. Besides, from the perspectives of electric field distribution, defect detection mechanism, and equipment applicability, technical principles of AC and DC withstand voltage tests were compared. By calculating the current on non-metallic outer sheath of 110 kV, 630 mm² and 220 kV, 2500 mm² cables, it was verified that leakage current on non-metallic outer sheath of the cables under DC withstand voltage test was in microampere range. Due to its high sensitivity, portability of equipment, and precise identification ability for local defects, DC withstand voltage test could become the preferred method for electrical performance inspection of non-metallic outer sheath of high voltage cables.