Hello Amirali1383koohi,
"난 학생 이다" kinda sounds like a declaration of some sort that you wouldn't really employ in an everday conversation.
The "-이다" ending sounds rather literary, and personally, I find it kinda solemn, if you know what I mean haha.
If you are looking for a more colloquial way of conveying the same idea, you'd say, "전 학생이에요 (polite)" or "난 학생이야 (casual)".