Thanks very much. I tried your lines. But it reports:
cp: /mnt/mmc1/DOOM1.WAD: No such file or dictory
I changed mmc1 to mmc2 and got same problem. The file "DOOM1.WAD" was saved directly on the memory card and I can saw it in through file manager. Mine is 770 boot from mmc. Please give me some further instructions. Thanks!