1. A method for retrieving an external SD card, wherein the method comprises: Step S 1 , obtaining a loading paths list; Step S 2 , making the first loading path in the loading paths list as a current information record; Step S 3 , determining whether the current information record meets a filter criterion, if yes, executing Step S 4 ; otherwise, executing Step S 9 ; Step S 4 , detaching/splitting the current information record into a plurality of paths with a space, and making the first path as a current path of the current information record; Step S 5 , determining whether any preset character string is included in the current path, if yes, executing Step S 6 ; otherwise, executing Step S 7 ; Step S 6 , recording the current path and making it as a suspected external SD card path, then executing Step S 7 ; Step S 7 , determining whether any unprocessed path exists in the current information record, if yes, executing Step S 8 ; otherwise, executing Step S 9 ; Step S 8 , making the next path as the current path of the current information record, then returning to Step S 5 ; Step S 9 , determining whether any unprocessed loading path exists in the loading paths list, if yes, executing Step S 10 ; otherwise, executing Step S 11 ; Step S 10 , making the next loading path in the loading paths list as a current information record, then returning to Step S 3 ; Step S 11 , determining whether any suspected external SD card is recorded, if yes, executing Step S 12 ; otherwise, a final external SD card is not found; and Step S 12 , determining whether the final external SD card path exists in the recorded suspected external SD card paths, if yes, the final external SD card is found; otherwise, the final external SD card is not found.