Influence of equal channel angular pressing (ECAP) on mechanical properties of a TWIP steel was studied, and the tensile true stress-strain curves of the steel were fitted by Ludwik, Hollomon and Swift three kinds of constitutive model. The results show that the yield strength and ultimate tensile strength of the sample increase whereas ductility and tensile toughness decrease with the increasing number of ECAP passes. There is a good agreement between fitting curve of Ludwik, Hollomon, Swift model and the experimental curve. The fitting parameters of the each model are given in current paper, and the reason of the strain hardening exponent n decreases with the increasing of the ECAP pass is discussed.