Abstract: The mechanical properties and microstructure of plastically deformed Fe-Mn-C and Fe-Mn-Si-AI series high manganese twinning induced plasticity (TWIP) steels were investigated at different strains. The roles of TWIP effect in the two series TWIP steels were analyzed so as to clarify the strengthening mechanisms. It is found that the two series TWIP steels have high work hardening ability, while the work hardening ability of Fe-Mn-C TWIP steel with a lower stacking fault energy (SFE) is stronger. The two series TWIP steels deformed under the same conditions exhibit different work hardening rates, since different deformation mechanisms play a leading role during different deformation stages. There is a strong correlation between the microstructure morphology and the work hardening behavior. Multiplication of dislocations and generation of deformation twins have obvious effect on the work hardening index curves of the two series TWIP steels. In high-strain stages, the plenty of primary deformation twins T1 and secondary deformation twins T2 in Fe-Mn-C TWIP steel and high-density dislocation areas adhering to twin boundaries lead to its high work hardening ability. But the close-set primary deformation twins T1 and dislocations between twins are the reasons for the high work hardening behavior of Fe-Mn-Si-Al TWIP steel, whose microstructure is more uniform and finer.