Artagnan1978,Wige,DONtk and Iggyjac,
Thank you for your advice.Actually,when Googlebot recrawls the outdated pages,they return a status of 404 in the header.Then,Googlebot knows that the requested URL isn't valid and deletes the pages info from its database.For google,nothing special,just takes a long time to completely delete so many pages.Google presents a useful tool that makes it possible for webmaster to remove the outdated pages quickly.
See:
https://www.google.com/support/bin/answer.py?answer=508...lev=answer
---