In gg Webmaster Tool, I can check the keywords indexed by gg on my sites. But some words are just codes or simple words have no meaning. I don't expect google to take these words as keywords. How can I do?
Google webmaster tools account will show all keywords which have been repeated many times on your site irrespective of how relevant or useful they might be.
I dont think you really could do much. Just check to make sure you have followed all the on-page SEO basics.
I wouldn't worry about Google counting extra words as keywords. I'd only worry if what I wanted to be keywords weren't counted as such.
Google keeps updating that keywords based on how frequently you update site or contents. Do not worry about them much. The words which you want the people to include in their search , keep writing about those topics. My keywords page was blank for a month but analytics was showing me visitors.
<!-- google_ad_section_start --> good keywords here <!-- google_ad_section_end --> <!-- google_ad_section_start(weight=ignore) --> bad keywords here <!-- google_ad_section_end(weight=ignore) -->
what about your main keyword? If it has been count as keyword, that's fine. And add more content around your main keywords to let google know that is your main keywords.
This does, of course, only work in terms of how adsense evaluates your page, not the general search googlebot.