Designs a battery management system with ARM STM32 processor as the main control chip and uC/OS-II real-time operating system for task scheduling implementation. It includes lithium battery parameter collecting module, balancing module, controller area network communication module and charge and discharge control module. The parameters of voltage, temperature and current gathered from the lithium battery parameter collection module communicate with the main control chip through CAN bus. Based on the sampling parameters, the main control chip controls the battery energy equilibrium, protects the security of the battery, estimates the battery state of charge and displays the information of current, voltage, temperature and state of charge on LCD. The system estimates the battery state of charge accurately, achieves the balance between multiple batteries quickly and has good extensibility.