Add more content.

Use the section targeting guides provided by adsense:

[google.com...]

And wait. It took over a year for me to get the kind of *really* focused, targeted ads I wanted, but eventually I got 'em, and the epc's rose remarkably.

Look in your web server log files to see if AdSense's bot has visited your whole site - and not just your home page.

Look for the following as the user agent:

Mediapartners-Google

This not the same as being crawled by the Googlebot; that indexes your site for the search engine, but it's Mediapartners-Google that examines your content to find keywords to use for context-sensitive ads.

It can also happen that some bug in the AdSense server at Google screws up your relevancy; if you find that you have already been crawled by the Mediapartners bot, I'd contact AdSense support to ask about it.

I have a very popular page that consistently gets ads for a certain kind of product, but one day I found that every ad on the page was for a certain very different kind of product that had nothing whatsoever to do with the content on the page. A mail to AdSense support got it fixed.

thanks..do you think how i build my site affect it ?
I mean I use those pre-defined sitebuilder provided by my webhost to build my site. Despite I have built many sub-sections and many pages all about baby, the ad it shows only relate to my domain name which unfortunately has nothing to do with baby.