Focused on the voltage drop and energy loss of metallized film pulse capacitor in actual use, which leads to the decreases of stored energy and energy density of pulsed power supply during the long voltage holding process after charging, based on the experimental data of a high voltage and high capacity pulse capacitor and the relationship between conductivity characteristics, self-healing characteristics, polarization characteristics and energy loss, the quantitative relationship between conductivity and voltage drop was derived and the conductivity measurement was carried out, the quantitative relationship between self-healing and voltage drop was derived and the life test was conducted, the quantitative relationship between relaxation polarization and voltage drop was described and the simulation was completed. The results show that the proportions of dielectric leakage, self-healing and relaxation polarization in voltage drop are 29.6%, 11.75% and 58.35%, respectively. The main factor which leads to voltage drop is relaxation polarization.