I want to install KDE 4.6 on RedFlag Linux Desktop 6 SP3.
RedFlag Linux Desktop 6 SP3 detail:

kernel-2.6.31-4 , KDE 3.5.10 .

I want to install KDE 4.6 on RedFlag Linux Desktop 6 SP3, and how to do ?

If you wish it pre-packaged you'll need to search RedFlag at their site or forum, if you want to compile from source you can start here http://techbase.kde.org/Getting_Started/Build

According to DestroWatch.com RedFlag 7.0 ships with kde 4.2.2

But 6.0 used KDE 3.5.10 .

you have 2 choices

1) you can go to the RedFlag website and search for the 4.6.1 packages, if it's not apparent they are available you can ask in their forum(s) if they exist and if so where.

2) you can compile KDE 4.6.1 from source

KDE version availability is decided by the distribution and their packagers not by KDE, KDE only supplies the source code

En.I'll compile it myself.