With the popularization of new energy vehicles, in response to the market's increasing requirements for battery management systems, BMS (Battery management system) applied to pure electric vehicles has been designed. The system takes both cost and function into consideration, with STM32 single-chip microcomputer as the main control chip, using analog front-end chip, real-time detection of monomer and overall voltage. The thermistor is matched with a multiplexer to realize single point temperature collection. The Hall element can collect current information in a non-contact manner. The equalizing circuit automatically equalizes the capacity difference between the batteries according to the information collected by the system. In addition, the system also has insulation detection and communication functions. Use the extended Kalman filter algorithm to estimate the system SOC. Research experiments show that the system has high accuracy and reliability for voltage, current and temperature detection and SOC parameter estimation, which improves battery safety and efficiency. The system has complete and reliable functions, and has certain practical engineering significance.