Now I just found svn merge is so powerful.
If you just want to merge one pic of change from trunk to branch, you don't have to do the
svnmerge.py merge ...
You can just type in you working copy directory
svn merge -c VERSION YOUR_TRUNK_URL [WCPATH]
If you want to revert the change for the svn server side , not just your working copy
svn merge -rVERSION:VERSION-1 SOURCE [WCPATH]