Power battery is one of key parts in electrical vehicle. In order to obtain the on-site status data of power battery and provide a reference for optimizing the control parameters, this pater designed a 2G-capacity BMS on-site data storage system with SD memory card. It communicated with SD card in high speed SPI and used hierarchical driver model of SD card. The data was saved in FAT32 format, which could keep compatible with PC operating system. The experiment shows that the system has good real-time capability and high reliability.