Self-healing metallized film capacitor is widely used in modular multilevel converters (MMC), owing to its high power density, long life, high reliability. Temperature become a hot research topic as the main influencing factors of the stability and life of power capacitor. Based on actual engineering practice of VSC-HVDC, this paper has discussed the thermal stress of capacitor in its operating condition. A 3D temperature field model of metallized film capacitor is formulated based on finite element simulation tool COMSOL, and the temperature rise characteristics of the metallized film capacitor were analyzed and tested. According to the research results, the current stress and voltage stress of the metallized film capacitor in the MMC converters are relatively complex compound variables; The most hot spot is inside the element, the highest temperature rise is11.1℃ , the most hot spot of the shell is on the side, and the highest temperature rise is7.75℃. It provides reference for the operation and maintenance of the metallized film capacitor in the MMC converters.