The mechanical property and forming limit experiments were carried out on a high manganese TRIP/TWIP steels with manganese of 18.8%.And the forming limit diagram was obtained.This high manganese steel shows outstanding mechanical properties combining high strength with good formability.Its limit plane strain corresponding to the lowest point in the plain strain condition is about 38%.The effects of conventional mechanical property on the limit plane strain were analyzed.With increasing the content of Mn,the limit plane strain increases,indicating that TWIP effect is advantageous to the increase of formability.Combining with three classical models and volume invariable principle,a FLD model was built,which is suitable for high manganese steels very well. The mechanical property and forming limit experiments were carried out on a high manganese TRIP / TWIP steels with manganese of 18.8% .And the forming limit diagram was was.This high manganese steel shows outstanding mechanical properties combining high strength with good formability .Its limit plane strain corresponding to the lowest point in the plain strain condition is about 38%. effects of conventional mechanical property on the limit plane strain were analyzed. Increasing the content of Mn, the limit plane strain increases, indicating that TWIP effect is advantageous to the increase of formability. Combining with three classical models and volume invariable principle, a FLD model was built, which is suitable for high manganese steels very well.