The invention discloses a battery management system of a vehicle-mounted lithium power battery. The system includes a master control unit and slave control units. The master control unit is in communication connection with the multiple slave control units through a data bus. The master control unit is in connection with battery groups, the total voltage and total current of which are acquired. The master control unit is also connected to a DC power supply, and is in connection with a charger through an external CAN bus. The master control unit mainly includes: a master microcontroller module, a total voltage detection module, a total current detection module, a battery system insulation detection module, a battery operating environment temperature detection module, a relay driving module, a data storage module, a bus communication module, an isolated power supply module, and a physical interface module of power supplies, data, signals, etc. The system provided in the invention has the advantages of simple structure, strong expansibility, and adaptability to different numbers of batteries. Being fully functional, the system has the functions of temperature control, equalization processing, battery performance evaluation, and battery self-protection, etc.