As a key component of modular multi-level converter (MMC), metallized film capacitor has the advantages of good reliability, high energy storage density and high working field strength. The failure of capacitors will affect the safe operation of the converter and even the even VSC-HVDC transmission systems. AC and DC accelerated aging test platforms are set up, and get aging samples through accelerated aging test. The aging characteristics of metallized film capacitors under different electrical stress are obtained by scanning electron microscope and confocal microscope. The results show that due to the different degradation mechanism of capacitors under different kind of voltages, the rule of capacitance value′s ruducing and the morphology of degradation point are obviously different. Through accelerated aging test, the typical morphology characteristics of the degradation point of capacitors under AC and DC voltage are obtained, which can further analyze the degradation mechanism of metallized film capacitors. The research has practical value.