[root@localhost dev]# uname -a
Linux localhost.localdomain 2.6.32.23-170.fc12.i686.PAE #1 SMP Mon Sep 27 17:40:41 UTC 2010 i686 i686 i386 GNU/Linux

[root@localhost dev]# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda3 20158332 8998820 10135512 48% /
tmpfs 1013220 624 1012596 1% /dev/shm
/dev/sda5 153605464 67358256 86247208 44% /D
/dev/sda6 153605464 146477104 7128360 96% /E
/dev/sda7 128953720 25809672 103144048 21% /F

I don't know why "hibernate" disappear.It has swap on my fedora before.But I delete swap partition by accident.Does my problem has something related to this?
Anything help will be appreciated.

i guess it related only to kernel version / recent update. happens on my system very often, i don't care.

I think you're right.I updated fedora recently.
But how can I get this back?

try to find right kernel for you or build from source (kernel.org)

My kernel version: 2.6.32.23-170.fc12.i686.PAE
Doesn't it support hibernation?

i belive all kernels supports hibernation, but related to bugs/chips it can temporary drop it.