The invention provides a method and a device for on-line maintenance of a battery pack. The method comprises the following steps: when an instruction for maintaining the battery pack is received, judging whether a DC power supply module is normal or not; Wherein, the DC power supply module is used for supplying power to the DC bus bar corresponding to the battery pack during the maintenance of thebattery pack; If yes, the battery pack is charged and discharged by a charger and an active inverter unit corresponding to the battery pack; When the charge/discharge maintenance is complete, restorethe battery pack to its initial operating condition. The invention can supply power to the DC bus bar corresponding to the maintained battery pack through the DC power supply module during the maintenance of the battery pack, thereby improving the power supply reliability of the DC bus bar during the maintenance of the battery pack, and further contributing to improving the reliability of the on-line maintenance method of the battery pack.