High manganese steels demonstrate significant potential for industrial application due to their remarkable TRIP/TWIP effects at room temperature. Thus, they attract interest of many researchers. In this work, mechanical properties and microstructure evolutions of an Fe－22Mn－3Si－2Al TRIP/TWIP steel after tensile deformation were studied by mechanical tests and SEM analysis, and in particular, the crystallography of martensitic transformation was analyzed by EBSD technique. The results show that, plenty of harder thermalε－martensite existed before deformation and transformed to α’ －martensite during tensile deformation, namely the two kinds of martensite transformed asynchronously. During deformation, the TRIP effect by strain induced α’－martensite and the TWIP effect by deformation twinning coexisted, leading to good combination of strength and ductility in this steel, and furthermore, ε－martensite didn't cause the low temperature brittleness. The thermal ε－martensite showed tilting basal texture. When deformed,basal slip was an easy activity, whereas deformation twinning of 86°<1120> was also detected, which sometimes revealed 93°<7253> relationships by a combination of 30°<0001> misorientation due to mis－indexing of pseudosymmetry during EBSD measurement. During tensile deformation α’－martensite revealed a rotation around crystallographic <110> axis and scattered orientations, forming the phenomenon of comets trailing. Besides, austenitic orientations also rotated and increased low angle misorientations. And annealing twins in austenite was found to facilitate the martensitic transformation.