It is said that edgar allan poe speaks in annabel lee about his wife verginia,but he said tha it is a maiden .Why?

A poem doesn't need to mention the person's name to be about that person. Poems are very personal and intentionally cryptic. You are correct, most scholars think Poe is referring to his wife Virginia but, like all good poetry, it is open to interpretation. Check out my link and scroll down to "inspiration".

http://en.wikipedia.org/wiki/Annabel_Lee