This application discloses a method for upgrading an energy storage system, and an energy management system. The method includes: obtaining a to-be-upgraded file of the energy storage system; controlling the energy storage system to disconnect from high voltage when a current operating status of the energy storage system allows a program upgrade; detecting status of high voltage connection of the energy storage system; receiving a notification sent by a battery management system in the energy storage system indicating completion of disconnecting the energy storage system from the high voltage; and sending the to-be-upgraded file to the battery management system to perform the program upgrade according to the to-be-upgraded file.