Thanks for all of you!
With so many welcomes and responses, I do feel I am a member in a big family.
After I submitted a wrong url without corresponding site to search engines, my clients got the wrong url as their search results from google. When they click the url listed in the search results, the page can't be displayed because there is no web site associated with the url. I just hope the url will be deleted the next time google trying to use the url to crawl the non-existing site.
I have visited google remove url page. In my understanding, the removal only applies to an url which has a web site.
I am not sure if I am right or not.