Thank you Brian :) Just found that the cellclickaction of the tree I am working on is set to be "edit" mode, which prevents the drag operation happen. may be I should think in another way to solve my probelm, thank you anyway: )

An instance of the Infragistics.Win.UltraWinTree.Override class is exposed via a property named 'Override' by UltraTree, UltraTree.NodeLevelOverrides, UltraTree.Nodes, and each individual node (UltraTreeNode.Override). The Infragistics.Win.UltraWinTree.Override class exposes the properties I mentioned originally.

CellClickAction is a property, not an event; if you search your source code for "CellClickAction", I expect you will find that it is set to some value that interferes with dragging. If not, you should report this issue so that you can provide a test project that demonstrates the problem you are experiencing.

Sorry, which control do you mean for "the Override object"? while the ultree itseld has not CellClickAction event, Could you send me your practice code you made for my question ? thank you :) 

SelectionDragStart only fires when a selected node is dragged, but I just verified that this also works correctly when cells are displayed. The two relevant properties here are the CellClickAction and SelectionType properties of the Override object. CellClickAction basically tells the tree what to do when the user clicks on a cell; you cannot use the 'EditCell' or 'EditCellSelectText' settings and get the SelectionDragStart event to fire because when the user presses the mouse button, it puts the cell into edit mode, thus precluding a drag operation. The SelectionType property, when set to 'ExtendedAutoDrag', tells the control whether to go right into a drag operation when the mouse is moved while the left button is pressed; when set to 'Extended', you have to release the mouse button after the selection, then the next click and drag initiates the drag operation.

Brian, Do you know where can get the implementation code of selectiondragstart of UltraTree?

I met a problem about the dragdrop behavior in ultratree, here is the detail:

In the ultratree I create, each tree node is displayed with two cells, which makes the tree looks like a table with two columns.

now we want the drag operation can be started when either of the cells of a tree node or a row of the tree(which is actually a tree node selected )  selected and draged,  while the selectionDragStart event can only be fired when a row of the tree selected, how can we make the drag operation fired when eithe cell of a tree node selected? Thank you in advance :)