How to disable prompt when dragging files?

By editing configuration files? Or by changing a certain check-box of preference dialog?

Which prompt are you referring to?
Are you referring to the Folder View menu which offers move, copy and link options which appears when drag+dropping files?

Yes. I meant the prompt which ask me to move or copy or link.

Unfortunately it is not possible to disable this prompt/menu - because the exact intention of the user is not known when performing the drag and drop action.

I just want KDE to behave like Gnome, who doesn't provide this prompt.

For gnome and Windows, if user drag a file within the same harddisk partition, the system will move the file, if the user drag the file to a different partition, the system will copy the file.

Whenever I drag a file within the same partition, KDE prompt for confirmation. It is very annoying.

KDE at least should provide an option to turn it off since not all the users like this feature.

Unfortunately an option does not exist at this time. You could try filing a feature request at bugs.kde.org however.