Abstract: After a capacitor is charged to the set voltage and disconnected from the power supply, the voltage decay will occur, resulting in the decrease of discharge efficiency. Taking metallized polypropylene film capacitor (MPPFC) as the object, we studied the influence of crystallinity on the voltage maintaining performance of capacitors. The trap parameters were obtained by using thermally stimulated depolarization current method, and a voltage maintaining performance experiment platform of MPPFC was built to study the voltage maintaining performance of MPPFC with different crystallinity. The results show that, with the increase of crystallinity, the conductivity of polypropylene film decreases, the number of relaxation polarization branches decreases, the trap depth becomes shallower, and the voltage maintaining performance of MPPFC is enhanced. BOPP films with higher crystallinity have lower conductivity and less dielectric leakage. Moreover, the increase of crystallinity will change the relaxation polarization process and correspondingly the voltage decay will decrease. Appropriately increasing the crystallinity of the dielectric film can improve the voltage maintaining performance of metallized film capacitors.