An improved maintenance method of a power battery pack is disclosed herein, comprising the following steps: (1) conducting analysis on battery pack; (2) data preprocessing; (3) conducting normalization processing of voltage data volavgi obtained in (2) and state of charge SOCi, state of health SOHi of single cells respectively; (4) calculating the charging and discharging levels of single cell that needs to maintain, and determining the battery sets that require charging and discharging maintenance. The maintenance method of power battery pack in the invention can perform analysis of various characteristic data of battery in a real-time manner and pick up the single cells that need charging and discharging maintenance during battery pack operation, and control the ratio of number of batteries that need charging maintenance to that needs discharging maintenance, to achieve bus balance.