Capacitors are important storage components in pulsed power equipment. In order to reduce the volume of the power source equipment, the energy storage density of the capacitors must be increased. This paper describes the basic breakdown mechanism of capacitors. To avoid the disadvantage of film-foil type capacitors, the authors present two new techniques, which are metallized film structure and mixed-film structure. The energy density of two kinds of capacitors is over 500J/L.