Precharging device for electric vehicle and precharging method of precharging device

The invention provides a precharging device for an electric vehicle and a precharging method of the precharging device. The precharging device comprises precharging subcircuits connected in parallel to two ends of a main relay and a precharging auxiliary device connected to positive and negative electrodes of a direct current bus and further comprises an electronic control unit, a bi-way DC/DC converting circuit and an energy storage capacitor, wherein the electronic control unit is used for receiving a direct current bus voltage signal, an energy storage capacitor voltage signal and a power battery voltage signal and controls charge and discharge of the energy storage capacitor in the precharging process; the bi-way DC/DC converting circuit is used for transmitting electric energy from a power battery to the energy storage capacitor for charging when a precharging relay is turned off under the control of the electronic control unit, discharging the energy storage capacitor when the voltage of the energy stor