Abstract: The power connector is a key component in the traction power supply system of metro vehicles, which insulator is continuously subjected to electrical and thermal stresses, therefore, weak regions of the insulator are highly susceptible to degradation and even failure. However, the insulation degradation characteristics and mechanism for metro vehicle power connectors are still unclear by far. A type of power connector commonly used in metro vehicles is studied. The electro-thermal accelerated aging tests are conducted under different temperature conditions based on actual service environments, the degradation & damage characteristics at different aging stages are investigated, and insulation resistance evolution is obtained. By combining the finite element simulation results of the electric field distribution, the degradation mechanism of the connector insulator is discussed. Results show that insulation degradation of the power connector initiates from the grounding clip region, where local electric field enhancement induces partial discharges. Long-term partial discharge leads to surface degradation of the insulator, and with prolonged aging time, the degraded region gradually expands and the degradation channel deepens, eventually resulting in breakdown failure. Further, it is discovered that the deteriorated region area is positively correlated with the duration and degree of insulation deterioration, which could be used as a quantitative characterization parameter for the deteriorated state. Moreover, environmental temperature has a significant effect on the degradation process, that defect propagation and insulation performance deterioration are markedly accelerated under high-temperature conditions. This study reveals the degradation evolution process and underlying mechanism of the power connector insulator, which provides important technical insights for the reliability assessment of electrical insulation in metro vehicles.