1. How can I build robot by xith3d ? I hava a problem that xith3d is not allow to add the same node to different parent. But I need the robot that can move at any joint and the other joint will move too.
Well, the fact that you can't add same node to different parents in Xith surelly doesn't do any limitation for you.
BTW, have you seen that possible in other APIs? ... just sounds strange to me such a "feature" because it is braking my understanding of scenagraph on its parent-to-child relations...

Anyhow, if you have on the mind "sharing the node" in the sence of sharing the geometry & appearance to avoid extra memory allocation xith's node.sharedCopy() (or Shape3D.sharedCopy()) will do the trick for you.
2. If I build graphic from xith3d, Are they can be integrate to odejava ? I have seen the example that map cube in xith3d to geombox in odejava, but if I use my own shapes.Can I still map them from xith3d to odejava?
3. I'd like to see the example project not the basic but something similar to me, Can anyone give me a suggestion?
Well, I can't advice on that really, as I never tried odejava myself, but William Dennis (do search for his posts, see
http://www.java-gaming.org/forums/index.php?topic=10386.0 for instance) was successfully using it in his projects (see
http://williamdenniss.com/lineriders/ for instance).
Anyhow, as far as my understanding goes you can always do you own mapping!...
sorry for my bad english.
your english is good enough, not much worse that mine

, so no worries
Bohdan.