I found that as a regular user run fsck in multi user model will show me a terrible result. 
But, if I reboot and run fsck in single user modle, the system will tell me everything is ok.
Code:
> fsck
** /dev/ad12s1a (NO WRITE)
** Last Mounted on /
** Root file system
** Phase 1 - Check Blocks and Sizes
** Phase 2 - Check Pathnames
** Phase 3 - Check Connectivity
** Phase 4 - Check Reference Counts
** Phase 5 - Check Cyl groups
647 files, 20650 used, 233165 free (781 frags, 29048 blocks, 0.3% fragmentation)
** /dev/ad12s1h (NO WRITE)
** Last Mounted on /home
** Phase 1 - Check Blocks and Sizes
INCORRECT BLOCK COUNT I=27957309 (4352 should be 384)
CORRECT? no
** Phase 2 - Check Pathnames
** Phase 3 - Check Connectivity
** Phase 4 - Check Reference Counts
UNREF FILE I=27957307 OWNER=fender MODE=100600
SIZE=4204 MTIME=Apr 20 20:08 2010
RECONNECT? no
CLEAR? no
UNREF FILE I=27957309 OWNER=fender MODE=100644
SIZE=2204360 MTIME=Apr 20 20:08 2010
RECONNECT? no
CLEAR? no
LINK COUNT FILE I=27957310 OWNER=fender MODE=100600
SIZE=4204 MTIME=Apr 20 20:08 2010 COUNT 2 SHOULD BE 1
ADJUST? no
** Phase 5 - Check Cyl groups
FREE BLK COUNT(S) WRONG IN SUPERBLK
SALVAGE? no
SUMMARY INFORMATION BAD
SALVAGE? no
BLK(S) MISSING IN BIT MAPS
SALVAGE? no
4465 files, 570442 used, 123880835 free (355 frags, 15485060 blocks, 0.0% fragmentation)
** /dev/ad12s1d (NO WRITE)
** Last Mounted on /mnt
** Phase 1 - Check Blocks and Sizes
** Phase 2 - Check Pathnames
** Phase 3 - Check Connectivity
** Phase 4 - Check Reference Counts
** Phase 5 - Check Cyl groups
6 files, 6 used, 253809 free (41 frags, 31721 blocks, 0.0% fragmentation)
** /dev/ad12s1f (NO WRITE)
** Last Mounted on /tmp
** Phase 1 - Check Blocks and Sizes
** Phase 2 - Check Pathnames
** Phase 3 - Check Connectivity
** Phase 4 - Check Reference Counts
** Phase 5 - Check Cyl groups
20 files, 12 used, 2029019 free (75 frags, 253618 blocks, 0.0% fragmentation)
** /dev/ad12s1g (NO WRITE)
** Last Mounted on /usr
** Phase 1 - Check Blocks and Sizes
** Phase 2 - Check Pathnames
** Phase 3 - Check Connectivity
** Phase 4 - Check Reference Counts
** Phase 5 - Check Cyl groups
314089 files, 2047841 used, 18263557 free (26301 frags, 2279657 blocks, 0.1% fragmentation)
** /dev/ad12s1e (NO WRITE)
** Last Mounted on /var
** Phase 1 - Check Blocks and Sizes
** Phase 2 - Check Pathnames
** Phase 3 - Check Connectivity
** Phase 4 - Check Reference Counts
UNREF FILE I=377015 OWNER=fender MODE=100600
SIZE=6532 MTIME=Apr 20 20:09 2010
CLEAR? no
UNREF FILE I=377017 OWNER=fender MODE=100600
SIZE=2688 MTIME=Apr 20 20:09 2010
CLEAR? no
UNREF FILE I=377018 OWNER=fender MODE=100600
SIZE=2368 MTIME=Apr 20 20:07 2010
CLEAR? no
** Phase 5 - Check Cyl groups
2556 files, 27602 used, 2001429 free (293 frags, 250142 blocks, 0.0% fragmentation)
>But, if I reboot and run fsck in single user modle, the system will tell me everything is ok.
