Microstructure and mechanical properties of two kinds of non-magnetic high manganese steels with and without Nb addition which experienced the same rolling and heating treatment were investigated by means of scanning electron microscopy,electron back-scattered diffraction,transmission electron microscopy,X-ray diffraction and tensile test.It was found that the microstructure of the high manganese steel was refined by the Nb addition.Moreover,steel with Nb addition has a higher stacking fault energy which favors the deformation twinning.Twinning is the most important deformation mechanism in the Nb-bearing steel.Therefore,steel with Nb addition has much higher strength and higher plasticity.The product of tensile strength and total elongation exceeds 61.8 GPa·%.In addition,steel with Nb addition also has excellent non-magnetic property. Microstructure and mechanical properties of two kinds of non-magnetic high manganese steels with and without Nb addition which experienced the same rolling and heating treatment were investigated by means of scanning electron microscopy, electron back-scattered diffraction, transmission electron microscopy, X-ray diffraction and tensile test .It was found that the microstructure of the high manganese steel was refined by the Nb addition .Moreover, steel with Nb addition has a higher stacking fault energy which favors the deformation twinning. Twining is the most important deformation mechanism in the Nb bearing steel with Nb addition has much higher strength and higher plasticity.The product of tensile strength and total elongation exceeds 61.8 GPa ·%. addition addition steel has also excellent non-magnetic property.