Google has explained new method to verify website ownership, Verification by DNS record. It allows you to become a verified owner of an entire domain (and all of the sites within that domain) at once. It also provides an alternative way to verify for folks who struggle with the existing HTML file or meta tag methods.
For example, if you have several websites under domain.com, including http://www.domain.com/, http://blog.domain.com/ and http://beta.domain.com/. You can individually verify ownership of each of those sites using the meta tag or HTML file method. But that means you need to go through the verification process three times, and if you wanted to add http://customers.domain.com/, you need to do it a fourth time. DNS record verification gives you a better way!
First you add domain.com to you account, either in Webmaster Tools or directly on the Verification Home page.
On the verification page, you will select the “Add a DNS record” verification method, and follow the instructions to add the specified TXT record to your domain’s DNS configuration.
When you click “Verify,” Google will check for the TXT record, and if it’s present, you will be a verified owner of domain.com and any associated websites and subdomains. Now you can use any of those sites in Webmaster Tools and other verification-enabled Google products without having to verify ownership of them individually.