OK, finally I got the answer by myself...
first thing we occured in this issue is got below warning when execute emulator.
WARNING: SD Card files must be at least 9MB, ignoring /dev/sdX
after traced the source code in main.c,
if (size < 9*1024*1024ULL) {
fprintf(stderr, "### WARNING: SD Card files must be at least 9MB, ignoring '%s'\n", opts->sdcard);
} else {
hw->hw_sdCard_path = ASTRDUP(opts->sdcard);
}
I ignored the if condition, i.e. force execute hw->hw_sdCard_path = ASTRDUP(opts->sdcard);
then, everything go right:)