Out of all the movies Titanic which one is real one?

There is only one Titanic movie, the one released in 1997. It's a fictionalized story, meaning while it's inspired by the real Titanic disaster, it's not a documentary and features characters and events that never happened.

There is, of course, the real Titanic, which was a British passenger liner that sank in the North Atlantic Ocean in 1912. You can find many documentaries and historical accounts about the actual tragedy, but the 1997 movie is not a documentary.