The invention provides a battery pack parallel connection operating method. The battery pack parallel connection operating method comprises a battery pack discharging step, wherein before a discharging process is implemented, all charging MOS transistors are in off-states, and all discharging MOS transistors are in on-states; all battery modules are connected in parallel through diodes in the charging MOS transistors in the allowed discharging direction; when discharging begins, the battery module with the highest voltage performs discharging firstly; and after discharging is completed, the discharging MOS transistors are in on-states while the charging MOS transistors are in off-states, wherein the states of the charging MOS transistors and the discharging MOS transistors are the same as the initial states of the charging MOS transistors and the discharging MOS transistors in the battery discharging step. By virtue of the method, on the basis of no over-charging and over-discharging, the problem of mutual charging and discharging caused by parallel connection of multiple battery modules can be solved by controlling the on-off of the charging MOS transistors and the discharging MOS transistors, and the problem caused by parallel connection of battery modules even with totally different types of voltage levels also can be solved.