The invention discloses a battery system and a starting control method thereof. The battery system comprises a pre-charging unit, M relays, M diodes, M battery packs and M battery management units, wherein the pre-charging unit comprises a pre-charging resistor and a pre-charging relay; first output ends of the M battery packs are connected with the first end of the pre-charging unit after being serially connected with the M relays in a correspondence manner, the first end of the pre-charging unit is connected onto a first output bus, and second output ends of the M battery packs are electrically connected with a second output bus; the first output ends of the M battery packs are serially connected with first ends of the M diodes, and second ends of the M diodes are connected with the second end of the pre-charging unit after being connected together; the M battery management units are connected with the M battery packs in a correspondence manner so as to acquire state information; and a battery control unit controls the pre-charging relays to be closed after being powered on to obtain a voltage sequence of the battery packs, and the M battery packs are controlled to start successively according to the voltage sequence after a preset time. By adopting the system, only one pre-charging resistor and one pre-charging relay are needed, so that the cost is decreased.