An electronic flash memory external storage method and device for data processing system includes firmware which directly controls the access of electronic storage media and implements standard interface functions, adopts particular reading and writing formats of the external storage media, receives power via USB, externally stores data by flash memory and access control circuit with the cooperation of the firmware and the driver with the operating system, and has write-protection so that the data can be safely transferred. The method according to present invention is highly efficient and all parts involved are assembled as a monolithic piece so that it has large-capacity with small size and high speed. The device operates in static state and is driven by software. It is plug-and-play and adapted to data processing system.