1. A method for retrieving an external SD card, wherein the method comprises: Step S1, obtaining a loading paths list; Step S2, making a first loading path in the loading paths list as a current information record; Step S3, determining whether the current information record meets a filter criterion, if yes, executing Step S4; otherwise, executing Step S9; Step S4, detaching/splitting the current information record into a plurality of paths with a space, and making a first path as a current path of the current information record; Step S5, determining whether any preset character string is included in the current path, if yes, executing Step S6; otherwise, executing Step S7; Step S6, recording the current path and making it as a suspected external SD card path, then executing Step S7; Step S7, determining whether any unprocessed path exists in the current information record, if yes, executing Step S8; otherwise, executing Step S9; Step S8, making the next path as the current path of the current information record, then returning to Step S5; Step S9, determining whether any unprocessed loading path exists in the loading paths list, if yes, executing Step S10; otherwise, executing Step S11; Step S10, making the next loading path in the loading paths list as a current information record, then returning to Step S3; Step S11, determining whether any suspected external SD card is recorded, if yes, executing Step S12; otherwise, a final external SD card is not found; and Step S12, 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.