everytime I start some app (especially large app) in my Arch system, the cursor will turn to a quite ugly icon like a watch or something. and I have changed the Xcurosr theme in my .Xresource to some other than default. but it still exist . how to solve this?
Not enough info I don't think.
Have you tried this Wiki entry?
The Using the XDG Icon Theme Specification method might work for you.