In this paper, a new method using a Secure Digital Card in debugging an embedded system based on Android and its implementation are introduced. In debugging an embedded system, downloading image files to a RAM on a printed circuit board generally uses a net interface module and a server based on Trivial File Transfer Protocol (TFTP). Here a new method using an SD card is introduced. Compared with downloading by a TFTP server, the method is simple and inexpensive. In the paper, an SD card and its controller are introduced first. Then the designed circuit is presented. Third, two operation modes of the SD card, card identification and data transferring are analyzed in detail. Fourth, the structure of the FAT32 file system and the process for downloading image files into a RAM on board are shown.