Abstract: To solve the thermal resistance bottleneck of isolated liquid-cooled cables for high-voltage fast charging systems of new energy vehicles and improve heat dissipation performance under high current-carrying conditions, two types of isolated liquid-cooled cable structures (indirect cooling type and copper-clad water type) were designed. High thermal conductivity modified cross-linked polyethylene (XLPE) tubes were used to replace conventional fluorinated ethylene propylene (FEP) tubes as cooling channels. 30-minute current-carrying temperature rise comparison tests were conducted by means of a temperature rise testing machine. 400 A and 700 A DC currents were applied to the two types of cables respectively, and the temperature rise characteristics under different tube material matches were monitored and analyzed. It was shown by the results that after the indirect cooling type cable was matched with the high thermal conductivity modified XLPE tube, the 30-minute temperature rise was reduced by 20.9 ℃ compared with the FEP tube sample; after the copper-clad water type cable was matched with the high thermal conductivity tube, the 30-minute temperature rise was reduced by 28.1 ℃ compared with the FEP tube sample. Significant heat dissipation enhancement effect was exhibited by the high thermal conductivity tube in both types of cable structures, and heat accumulation under high current-carrying conditions could be effectively alleviated. The thermal management capability of isolated liquid-cooled cables could be optimized by the formed cable structure design and high thermal conductivity tube selection scheme, reliable technical support could be provided for the performance upgrading and lightweight design of cables for high-power fast charging systems, and a positive role could be played in promoting the engineering application of high-voltage fast charging technology for new energy vehicles.