Abstract: A new reliability estimation algorithm for metallized film pulse capacitor was brought forward based on step-down stress accelerated degradation testing (SDSADT) method. The SDSADT was expounded, and the key procedure in the reliability estimation, i.e. testing data conversion, was fully explained. Then reliability assessment arithmetics based on pseudo failure lifetime and random degradation path were proposed. A numerical example was given to illustrate the algorithm. The results show that, at the same estimation precision, this algorithm can have a testing time 45% shorter than that based on constant sdtress accelerated degradation method.