My site is listed in Yahoo directory and I also submitted sitemap in yahoo-site-explorer. The sitemap is having 1245 pages but yahoo has indexed only 130 pages. I am unable to understand why yahoo is not indexing all the submitted pages. 
No search engine indexes all pages at one pass. Usually they spread it over time.
I guess you gotta give them some more time.
You have to wait for yahoo to do that. Search engines will not index whatever you send then instantly. 
but I added the site in yahoo site explorer 2 months before, then why am I facing this problem.
I think your sitemap need to be structured. A good sitemap with most important links given more preference and an easy linking to all other pages can help you better to get all your pages get indexed.
Unless of course it is a blog posting a new post, these usually appear within minutes in the index…