Abstract: Microstructure and mechanical properties of TWIP（twinning induced plasticity） steel before and after cold rolling deformation were investigated by optical microscope, transmission electron microscope, X-ray diffraction and tensile test system. The results show that the TWIP steel always maintains a single austenite phase before and after cold rolling deformation. Dislocation accumulation and a small amount of deformation twins are formed in austenite grains after 30% cold rolling deformation. Meanwhile, the interactions between the twins and dislocations begin to happen. When the deformation increases to 50%, a large number of deformed twins are formed, and the interaction between twins and dislocations is significantly enhanced. When the deformation reaches 70%, the austenite grains are refined to nanoscale, and ultrafine sub-grains are formed. With the increase of cold rolling deformation, the yield strength and tensile strength of TWIP steel increase, and the elongation after fracture decreases.