why do I always get crossed association for Ogrid
 

even if I re-associate the edge and vertex, the snap project vertices still goes crazy...

did I miss something when I split the Ogrid block?

Hi Guan Zhao,
The snap function does that. It doesnt give you a full representation of the object. It will 'work well' when you have objects like squares. If you really want the edges to represent the curves, select the spline option. I think it is under edit edge. Note though..this is only a graphical representation. It goes "crazy" graphically, yes but it still complies with what you're trying to do. One way to check is to put nodes on the edge and do a pre-mesh. Hope this helps. :)