The Melancholia director confirmed that he is currently writing the movie and may need to release it in two different versions, a hardcore edit and one suitable for mainstream release.
"As a cultural radical I can't make a film about the sexual evolution of a woman from zero to 50 without showing penetration. I know it's something very European," he joked to Entertainment Weekly.
Von Trier dismissed the idea that Nymphomaniac would be a porn movie, adding: "It principally is a film with a lot of sex in it and also a lot of philosophy."
His 2009 release Antichrist contained scenes of unsimulated sex, with porn actors standing in for stars Willem Dafoe and Charlotte Gainsbourg.
The Danish filmmaker announced Nymphomaniac at this year's Cannes, touting Kirsten Dunst as a potential star.
The Breaking the Waves director sparked controversy at the festival when he joked about being a Nazi. He was subsequently banned from the event, although Dunst won the 'Best Actress' accolade for her performance in Melancholia.
Watch the trailer for Lars von Trier and Kirsten Dunst's Melancholia below: