The invention discloses an active equalization method and an active equalization system for series-connected batteries. The method comprises the following steps of acquiring the voltage of each singlebattery, sorting the voltages of all single batteries to obtain a maximum voltage value and a minimum voltage value, dividing single batteries into groups based on the voltages of single batteries when a difference value between a maximum voltage value and a minimum voltage value is larger than or equal to a preset balance threshold value D, and charging/discharging the first/last group of singlebatteries so as to realize the active equalization effect according to the number of single batteries in the first group, the number of single batteries in the last group, and the current operation working condition of series-connected batteries. According to the invention, the effective and active equalization operation is conducted, so that the non-equalized problem of batteries is solved. Meanwhile, the active equalization of the large-current charging/discharging operation of series-connected batteries is realized. The energy is saved, and the service life of batteries is prolonged. The reliability of storage batteries in a direct-current system is improved. Moreover, the system is simple in structure and easy in modularization. A grouped stepping type active equalization strategy isrealized and then the consistency of a lithium battery pack can be effectively improved in different working conditions.