My emphasis added...
i have a lists for public holidays for diffrent countries...so in each post of each country public holidays, there are few necessery sentences that are most of the time the same for all other holiday posts.....is that a bad for SEO?
The idea of listing public holidays for various countries is a good one, and is useful for users. Google and other engines would expect a degree of templating on a site that covers multiple countries, so a templated introductory line or two is likely not to be an issue in itself.
The problem that all of the engines run into in assigning "ranking points" for such content, though, is that the information is essentially in the public domain, that it's perhaps been compiled many times before. Very probably, either now or in the future, many sites that take the "list" approach could well be returning the same lists.
So, the question is how far beyond
just a simple list are you going to go to make your pages which include such lists useful and informative for users... ie, how are you going to make your page stand out from all the others?
As I posted sometime after the MayDay update, back in July of 2010, in one of many discussions we were having about "thin" content, I don't think that lists alone are going to suffice.... Google Referals Down and Dropping More http://www.webmasterworld.com/google/4177890.htm
"Content" is no longer, I feel, about how many different ways you can sort the same pieces of data that many other people have too. While there are various takes on that model that may still be working, ultimately it's going to come down to unique content that's unique enough that it's valued by users and trusted by trusted sites.
Users and Google are, in the long run, going to value originality and additional depth of content. So, the problem you'll encounter may not be in the repetition of templated introductory text. It's liable to be that lists, by themselves, are likely to be too "thin"... and that pages constructed simply of lists aren't going to be sufficiently unique to compete.