Duplicate content on subdomain

[akorz]

I have duplicate content on few subdomains. Could it hurt site on main domain with unique content?

[tedster]

It could if, for instance, the subdomains begin to acquire backlinks. Then traffic might get sent to the subdomain and your main domain would be filtered. In extreme cases (such as wild card subdomains) your entire domain name - including all your hostnames - might fit a spam profile and get hurt on all search terms. That's rare but it does happen.

[Shaddows]

If you don't need traffic to go directly to those domains, you might consider using robots.txt to stop them being crawled and indexed. Or you could use the Prefered Domain option in Google Webmaster Tools.

But, unless you are being spammy (or appear to be spammy as per Tedster), all you need is a stronger backlink profile for the main domain and the rest are likely to just get filtered away.