Hi, it seems that KDE is not get along with IBus very well right? Now it appears to be good. I can work with it in Qt program by adding these lines to the bottem of ~/.profile

export GTK_IM_MODULE=ibus
export QT4_IM_MODULE=xim
export QT_IM_MODULE=xim
export XMODIFIERS=@im=ibus

But it can't work in Firefox. What should I do? Thank you.

Somehow now it works well on Firefox, but not in Qt. It seems that they can't both work well together?

It should simply be a case of setting the correct environment variables - QT4_IM_MODULE and QT_IM_MODULE should do the trick.
In terms of Firefox, it will probably respect the Gtk variables, given that it uses Gtk for parts of it's interface.

I change the value of QT4_IM_MODULE and QT_IM_MODULE to ibus but it still doesn't work.

Is the appropriate IBus Qt plugin installed? It will be called ibus-qt or similar.

After installing ibus-qt4, nothing changes.

Please run qtconfig and verify that no option in there needs to be enabled in order to ensure IBus support is enabled.

after install qt4-qtconfig, I can access to qtconfig. The only relevant selection in Qt Configuration is the Default Input Method in the Interface tab. Xim is the only one choice.

Does the directory /usr/lib64/qt4/plugins/inputmethods exist on your system, and if so, what files exist in it? (Change to /usr/lib/ if this is a 32 bit system).

It does not exist. Only designer and phonon_backend do.

Try to find the version of Qt, here it is:
ooker@ooker-Aspire-4741:~$ qmake -v
QMake version 2.01a
Using Qt version 4.8.4 in /usr/lib/i386-linux-gnu

Do I need to upgrade to Qt5? Will it mess everything?

Which distribution are you using? It appears that the Qt inputmethod plugin isn't included in the ibus-qt package...

In the About System:
KDELibs Version: 4.11.5
Qt Version: 4.8.4
Kernel Version: 3.11.0-19-generic

However...
ooker@ooker-Aspire-4741:~$ qmake -v
QMake version 3.0
Using Qt version 5.0.2 in /usr/lib/i386-linux-gnu

I just have installed Qt5 yesterday. Nothing changed. I now use Netrunner, the newest version.

Hi, sorry you've been having problems

If you still have your Kubuntu install could you check for
/usr/lib/*/qt4/plugins/inputmethods/libqtim-ibus.so ?

If you only have netrunner could you say how well it works there? There's no differences in netrunner on ibus setup compared to Kubuntu.

Well, I don't know how to check so I will post some useful commands:

ooker@ooker-Aspire-4741:~$ ls /usr/lib/*/qt4/plugins/inputmethods/libqtim-ibus.so
/usr/lib/i386-linux-gnu/qt4/plugins/inputmethods/libqtim-ibus.so

ooker@ooker-Aspire-4741:~$ sudo /usr/lib/*/qt4/plugins/inputmethods/libqtim-ibus.so
sudo: /usr/lib/i386-linux-gnu/qt4/plugins/inputmethods/libqtim-ibus.so: command not found

This indicates that the IBus Qt input method plugin does appear to be present on your system. Next question is why Qt is unable to find it - as it should be selectable from the drop down. Please see the "Initial Setup" section of https://wiki.archlinux.org/index.php/IBus