XLPE (cross-linked polyethylene) insulated cable is an important component of power transmission lines. In allusion to the operating status of HVAC and HVDC cables, the paper introduces the electrical ageing model of XLPE cable insulation based on the typical V-t characteristics (the relationship between breakdown voltage and breakdown time) and the research method of V-t characteristics both of HVAC and HVDC XLPE insulated cables. Previous research show that the electrical aging lifetime index n of AC XLPE cable is between 9 and 25, while the electrical aging lifetime index n of DC XLPE cable from very limted research shows that it’s between 13 and 20. And there is no research on V-t characteristics of DC cables having been reported yet in China.