Hi Jinfeng,
Have you looked into arcpy.mapping, the Python scripting module that allows you to update layers and automate PDF export? I suggest you start with this:
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//00s300000032000000
and this blog post has links to a variety of great resources and samples:
http://blogs.esri.com/dev/blogs/arcgisdesktop/archive/2010/09/24/getting-started-with-python-map-aut...
David