The director's long-delayed adaptation of F Scott's Fitzgerald's novel stars Leonardo DiCaprio as mysterious millionaire Jay Gatsby, and Tobey Maguire as Nick Carraway, a friend of Gatsby's and the novel's narrator.
"We know for a fact that if you read the whole book or perform it that it takes seven hours... so we had to make choices and we chose to stay very focused on the linear plot of the book," Luhrmann told Life+Times.
He went on to discuss the difficulty of adapting Carraway's narrative perspective.
"One of the big devices in the book is that the story is told from inside the mind of Nick Carraway... [he is] a watcher of and a participator in the story. In fact, in the novel, Fitzgerald very deftly alludes to the fact that Nick is writing a book about Jay Gatsby.
"How we do really is the one big difference in the film. I won't say how. I will let the audience discover that for themselves."
Carey Mulligan, Isla Fisher and Joel Edgerton also star in The Great Gatsby, which will open this year's Cannes Film Festival.
It will then be released in the US on May 10 and the UK on May 16.
Watch a trailer below: