Abstract: A memory extension apparatus and the method of data transfer applied therein. The memory extension apparatus comprises a first interface, a protocol converter, a processor, a file system, a memory unit, and a trigger unit. The protocol converter receives a first command from the first electronic device via the first interface for converting the same. The processor receives the converted first command from the protocol converter, and utilizes the file system to access the memory unit for files corresponding to the converted first command. The trigger unit is for triggering the processor to generate a second command, for accessing the first electronic device through a pre-defined protocol when the trigger unit is triggered. Without sacrificing size and weight of the first electronic device, the invention provides memory extension, file backup, and file sharing without the need of an external host device.