The invention discloses a capacitor and a preparation method thereof. The capacitor comprises a core, a conductor and a shell; the core comprises cathode foil, anode foil and electrolytic paper, and is internally impregnated with an electrolyte and provided with a conductive film; one end of the conductor is connected with the core, and the other end of the conductor is suspended; and the core isarranged in the shell. According to the capacitor and the preparation method thereof, the wound core of the capacitor is impregnated with macromolecular suspension liquid, and thus after the core is dried, a macromolecular film with high conductivity can be formed in the core to achieve low impedance of the capacitor; meanwhile, the capacitor after the macromolecular film is formed is impregnatedwith the electrolyte to repair an oxidation film of the anode aluminum foil, and thus the capacitor can have the very low leakage current value; and therefore, the capacitor has the lower ESR value, can withstand a larger ripple current, has the capacity for repairing the anode oxidation film, and is superior to a solid capacitor in withstand voltage storing capacity.