This paper presents the degradation testing and failure mechanisms analysis of metalized film capacitors used for AC filtering in MW power converters. Based on more than 2,800 hours of accelerated testing under accelerated AC voltage, temperature, and AC current, various electro-thermal parameter data are recorded. The results reveal that capacitance values have negligible reduction until the testing samples catastrophically fail. The capacitor hot spot temperature and case temperature are measured along the testing, which are increasing. The observations provide a new perspective on the possible failure mechanisms and condition monitoring of film capacitors in AC filtering applications.