The excellent combination of strength and elongation and the super work hardening behavior of high manganese TRIP/TWIP (transformation–induced plasticity/twinning–induced plasticity) steels are due to the presence of two kinds of martensitic transformations and their complicated interactions of three phases during deformation. This work investigated the crystallographic characteristics of γ →ε →α' transformation, and in particular, the effects of deformation twins and austenitic grain orientations on martensitic transformation by means of EBSD technique. Results showed that α'–martensite was triggered at the intersection of two ε-martensite variants. Deformation twins were frequently detected near ε–martensite, thus twins promoted the formation of ε–martensite and played n important role during TRIP pocess. However, twinning was affected by austenite grain orientations. It is suggested that austenitic grain orientations with low indices, such as {100}, {111} and {110}, more easily promoted the intersection of ε–variants due to the multi–twinning and thus facilitated further α′–martensite formation than those with high indices. Deformation increased the number of " variants but reduced their sizes and therefore it is difficult for the small strain–induced ε–martensites to transform into α′–martensites smoothly.