Home page deindexed by google

[semer]

when I search my website on google by site:www.mydomain.com

I have found my domain with www has been de-indexed by google,

but when I search site:mydomain.com,  my home page--**mydomain.com **show up on the search results without www,   put it simple, google only index my domain without www,

I wonder how to make my domain with www being indexed,

and how to prevent this problem occure again.

[SWKurt]

if you already haven't, make sure you look at adding a homepage canonical tag too

[AndreVanKets]

You cant have both versions indexed in Google. www and non www are 2 separate pages and seen as duplicate content if you use both.

As Google has already indexed the non www version, then I would redirect all your pages with www to pages without www to avoid duplicate content.

[DMGoo]

You will need to 301 redirect the none www version of your site to the www version.  By the sounds of things you are not using a CMS that will usually take care of this for you.

How you implement the redirect will be dependant on your webserver: linux apache or MS IIS.  Information for both can be found at the following URLs.  Keep me posted on how you get on.

Apache: http://jonsimpson.co.uk/log/2006/301_redirect_www_no_www

IIS: http://www.mcanerin.com/en/articles/301-redirect-iis.asp