How to login as root to Graphic Mode in CentOS 5.3?

It should be easy. Unlike some other distributions, root GUI login isn't automatically disabled.

So I think you need to tell use a bit more about your situation. (New install? Or picking up support for a server someone else customized? Or what?).

I have installed Centos 5.3 on a few systems. I don't recall exact details, but during the install process it asked for a root password, which I provided. Later in the install process, it rebooted and I logged in as root in GUI (Gnome) to customize the install. There was nothing tricky about logging in as root.

You can log with command line and then user "startx" to start Gnome. But using a root account for X is not a good idea, consider using sudo (I know how it sound, but it is true, it is really more secure and prevent accidents).

I know about security risk. But sometime I need GUI to do the job. I need full privilege in GUI to process. As I mention above, I'm running CentOS 5.3.

Is it possible to login GUI as root on CentOS 5.3?

Yes. I have done so several times. It required no special action compared to logging in GUI as an ordinary account.

I will assume you are responsible enough to exercise appropriate care while logged in GUI as root. You have seen the advice telling you not to do so at all. I can't say for sure that they are wrong. But I disagree with them.

Almost any system admin task that can be done via GUI could also be done by command line if you know how (I generally don't know how). Individual GUI programs can be run as root even while logged in GUI as non root. That is safer then having the whole GUI desktop root.

I personally balance the high probability of mistakes caused by being distracted by the extra overhead of doing things the "safer" way vs. the lower probability of doing something destructive in the side activities (anything that didn't really need to be root run during the necessary root activities). So I decide to use root GUI when I need to do any root activities that aren't easy otherwise.

But I do use and advise a dual login when doing something complex as GUI root that requires online searches for instructions or other details:

At work (using Centos and Windows) I use some form of remote desktop so the browser I use for searching the instructions is not on the same account nor even the same computer as the one on which I am using root GUI.

At home (Mepis) I just use Ctrl-Alt-F7/F8 to switch between a non root GUI running browser etc. and a root GUI running what needs to be root (and of course the desktop style is very different so I am constantly reminded which is which).

Are you getting any error messages? Did you try login?