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The deformation induced martensite and deformation twins were investigated by transmission electron microscopy (TEM) in high manganese TRIP/TWIP steels at different temperature. Because of the different temperature, the stacking fault energy (SFE) was different. It was pointed out that when SFE < 10.0 mJ/m3, deformation mechanism was the deformation induced bcc-martensitic transformation. When 17.7 mJ/m3 < SFE < 36.4 mJ/m3, the competition mechanism between deformation twins and hcp-martensite phase transformation was main deformation mechanism; when 36.4 mJ/m3 < SFE < 41.9 mJ/m3, the governing deformation mode was crystallographic slip and deformation twin; when 41.9 mJ/m3 < SFE < 78.3 mJ/m3, the slipping was a predominant deformation mode. The orientation relationships in the deformation process were obtained. It was found that the martensitic transformation from metastable austenite proceeded in two steps. In the first step, hcp-martensite nucleated at stacking faults of metastable austenite. And then the secondary hcp-martensite had been nucleated at stacking fault near deformation twins, and the bcc-martensite nucleated in the intersection of two hcp-martensite laths. The deformation nano-twins were observed to have been formed along the preferential hcp-martensite.